All DialogueActions variables are prefixed with "da." Further more, they contain periods - rarely used in variable names. This ensures DialogueActions variables do not mix with your normal dialogue variables.
For details about Object variables, see "About object variables.txt".
For details about Variable scopes in DA, see "About variable scopes.txt".

A listing of variables used by DialogueActions
FORMAT:
name {read only/write only/read and write} - explanation

da.bgm.volume {write only}. Range 0 (mute) to 1 (full volume, default). 0 mutes, 0.01 is the lowest audible setting. This sets the volume of the background music started with [PLAY_BGM_<filename>].

da.breathPercentage {read and write} - for her breath level (this drops first)
da.oxygenPercentage {read and write} - for her oxygen level (this drops when she starts passing out)

da.canSpeakLineTrigger {read only} - whether speak lines can trigger (based on gag, mouth full, passed out, and swallowing).

da.mouthfull {read only} - whether her mouth is full.

da.finishes {read only} - the amount of times he came, used in *FINISHES*.

da.masturbation.herpleasure {read and write} - her masturbation pleasure (scale: 0-100)
da.pleasurePercentage {read and write} - him pleasure (scale: 0-100)
da.clothes.<clothingType>.<colorComponent> {read and write} 
--clothingType = any of these: "ankleCuffs", "armwear", "bellyPiercing", "bottoms", "collar", "cuffs", "earring", "eyewear", "footwear", "gag", "headwear", "himBottoms", "himFootwear", "himTop", "legwear", "legwearB", "nipplePiercing", "panties", "tonguePiercing", "top", "tops"
--colorComponent = any of these: "r", "g", "b", "a", "r2", "g2", "b2", "a2". r, g, b and their r2, g2, b2 cousins are from 0 to 255. a and a2 are from 0 to 1
da.clothes.<clothingType> {read and write} - set a lot in one go. Formats: Type,R,G,B,A,R2,G2,B2,A2 OR Type,R,G,B,R2,G2,B2 (might set A and A2 to 1) OR Type,R,G,B,A OR Type,R,G,B - see the table below for which one you need
da.clothes.<clothingType>.type {read and write} - Set and get just the name of the clothing. So for the clothing type "top", you'll get things like "None", "Bra" or "Bikini". These refer to the names of the clothing items in the scene menu.
da.random {read only} - returns a random value between 0 and 1 (0 <= value < 1). Example usage to make it 1-10: (you'll have to define x as "*" in initial_settings to get access to multiplication operator) [VA_SET_VARIABLE_var1_*da.random x ( 10 - 1 + 1 ) \ 1 + 1*] - formula is ( random * ( max - min + 1 ) ) + min \ 1 + 1

da.hair.load {write only} - For loading hair files. Is a filereference, see "About Filereferences.txt" for more details. Only static images are supported right now. Delay set is possible, using [LOAD_HAIR]
da.background.load {write only} - For loading backgrounds. Is a filereference, see "About Filereferences.txt" for more details. Delay set is possible, using either [CHANGE_BACKGROUND] or [FADE_BACKGROUND_<hex>]
da.dialogue.load {write only} - For loading dialogues. Is a filereference, see "About Filereferences.txt" for more details. Acts instantly, might halt the current line from playing.
da.charcode.load {write only} - For loading (partial) charcodes. Is NOT a filereference, so you'll have to put the charcode in the dialogue.
da.mod.load {write only} - For loading mods. Must be trigger via the [LOAD_MOD] trigger after setting. Loads from the last loaded character folder.

da.dialogue.import {write only} - For importing dialogues. When importing dialogues, all the lines from the targeted file are added to the current dialogue. Is a filereference, see "About Filereferences.txt" for more details.

da.button<1-10>.name {write only} - For button names. Buttons that are enabled and have a non-empty string ("" = empty string) name will be displayed.
da.button<1-10>.varname {write only} - For button names. Acts as da.button<1-10>.name, but copies the value of a local variable at the time of setting.

da.blockingOrgasm {read and write} - related to [CUM_BLOCK_ON] and [CUM_BLOCK_OFF], this checks if the "orgasm block" is enabled or not. Returns 1 if cum block enabled, 0 otherwise. You can write 1 and 0 to this variable to trigger the same effects as [CUM_BLOCK_ON] and [CUM_BLOCK_OFF].

da.sdtoptions variables map to the options tab of the bottom ingame menu. Enabling such a feature acts as if the user had clicked the checkbox to enable the feature themselves.
All da.sdtoptions variables work like a boolean: For reading, they return 1 if enabled, 0 otherwise. You can write 1 and 0 to the variable to enable/disable (1 enable, 0 disable) the feature.
da.sdtoptions.hoverOptions {read and write} - For certain positions, this will be useful. Some people will not expect this to change, so perhaps record the variable at the start of your dialogue and put it back the way it was after you're done.
da.sdtoptions.showMouse {read and write} - For extra immersion - you might want to mention the use of this somewhere so people won't go "it breaks the mouse".
da.sdtoptions.strandShaders {read and write} - ... I don't know what this does.
da.sdtoptions.mirrored {read and write} - Mirrors the screen. Be careful with use in speech lines: this effectively moves the mouse to the other side of the screen. It might get violent.
da.sdtoptions.spit {read and write} - For enabling/disabling spit, a common lag source.
da.sdtoptions.tears {read and write} - Enables/disables tears.
da.sdtoptions.mascara {read and write} - In SDT, if tears are turned off, you can't turn on mascara. Except you can, and SDT just doesn't show it. It shouldn't do anything with tears off, though.
da.sdtoptions.smudging {read and write} - Enables/disables smudging.
da.sdtoptions.nostrilSpray {read and write} - ... nostril spray...
da.sdtoptions.sweat {read and write} - Enables/disables sweating. Note that if this is turned off, pussy dripping (via her masturbation or [PUSSYDRIP] trigger) won't occur, since it relies on a stream of sweatdrops.
da.sdtoptions.breathing {read and write} - Enables/disables breathing. If you turn breathing off, you can't make her pass out.
da.sdtoptions.gagging {read and write} - Enables/disables gagging. Gagging and coughing can interfere with speaking, so you could temporarily turn it off if needed.
da.sdtoptions.coughing {read and write} - Enables/disables coughing. Gagging and coughing can interfere with speaking, so you could temporarily turn it off if needed.
da.sdtoptions.tongue {read and write} - Enables/disables her tongue. If it's turned off, [TONGUE_OUT] and [TONGUE_IN] don't have any visual effect.
da.sdtoptions.dialogue {read and write} - Uhm... ... Yeah... Don't turn this off, it will cause DA to be useless. You could use this as the ultimate "Game Over" for a bundle - "I'll NEVER talk to you again!" that sort of stuff.
da.sdtoptions.invertControls {read and write} - If you turn it on and off repeatedly with some pauses with the mouse held back, she'll be all aggressive. Try 3-6 delay characters.
da.sdtoptions.bukkakeMode {read and write} - hey, a secret switch!

da.her.name {read only} - *ME* as a variable. Her character name. For example, "SD Chan".
da.her.namePossessive {read only} - *MY* as a variable. Her character name, plus 's. So "SD Chan's".
da.him.name {read only} - *YOU* as a variable. His name (the player's dialogue name). For example, "Bob".
da.him.namePossessive {read only} - *YOUR* as a variable. His name (the player's dialogue name), plus 's. For example, "Bob's".

da.her.clenchingTeeth {read only} - Whether she's clenching her teeth.

da.her.body variables control her body
da.her.body.breasts {read and write} - Controls her breast size. Scale goes from 0-149. It "pops" when setting, so recommend combining with [BOUNCE_TITS] to hide the instant growth, or use small increments. 
da.her.body.scale {read and write} - Controls her body scale. Goes from 0 to 1. I recall being able to go over 1, but SDT doesn't seem to play along.
da.her.body.hair {read and write} - For setting her hair. Values are the same strings shown in the in-game menu and can be expanded via MoreClothing. Doesn't reflect custom png hairs.
da.her.body.skin {read and write} - Controls her skin type. Values are "Light", "Pale", "Tan" and "Dark".
da.her.body.ears {read and write} - Controls her ear type. Values are "Normal", "Elf" and "Small".
da.her.body.nose {read and write} - Controls her nose type. Values are "Normal", "Pointed" and "Wedge".
da.her.body.iris {read and write} - Controls her iris type. Values are "Normal", "Bright", "Solid", "Blank", "Wide", "Sharp", "Flat", "Cat" and "Swirl".
da.her.body.eyebrow {read and write} - Controls her eyebrow type. Values are "Normal", "Crescent" and "Lines".
da.her.body.mascara {read and write} - Controls her ... mascara slider. Scale goes from 0 to 100. My best guess for the mascara slider is that it's the chance that a tear will cause a smear. There is no change in the intensity of the mascara. For intensity changes, try looking at the alpha colorcomponent.
da.her.body.freckles {read and write} - Controls the freckles on her face. Scale goes from 0 to 100. Rather than being a fade-in, freckles seem to work by drawing more freckles as the slider goes up.
da.her.body.penis {read and write} - Controls her penis type. Values are "None", "Penis A", "Penis B" and "Strapon".
da.her.body.penis.length {read and write} - Controls her penis length. Values range from 0.7 to 1.2 normally, but with mods this can change. See minSize and maxSize variables.
da.her.body.penis.width {read and write} - Controls her penis width. Values range from 0.7 to 1.2 normally, but with mods this can change. See minSize and maxSize variables.
da.her.body.penis.minSize {read only} - Retrieves her min penis size. Useful in combination with penisrange mod.
da.her.body.penis.maxSize {read only} - Retrieves her max penis size. Useful in combination with penisrange mod.
da.her.body.tan {read and write} - For setting her tan type. Values are "None", "Full", "Bikini", "Swimsuit" and "Swimsuit-T".
da.her.body.tan.amount {read and write} - For setting the amount of her tan - acts as an alpha factor for the tan sprite? Values range from 0 to 1.

da.him.ejaculating {read only} - Whether he's currently ejaculating. Values are "true" and "false".

da.him.body variables control his body
da.him.body.gender {read and write} - Controls his body type. Values are "Male" and "Female".
da.him.body.skin {read and write} - Controls his skin type. Values are, for the Male body, "Light" and "Dark"; for the Female body, "Light", "Pale", "Tan" and "Dark".
da.him.body.balls {read and write} - Controls his balls type. Values are "None" and "Normal".
da.him.body.balls.size {read and write} - Controls his balls size. Values range from 0.5 to 1.3, but mods may alter the minimum and maximum sizes.
da.him.body.breasts {read and write} - Controls his breast size. Values range from 1 to 149, but for the Male body, the value is always 0 since there are no breasts.
da.him.body.penis {read and write} - Controls his penis type. Values are "Penis A", "Penis B" and "Strapon".
da.him.body.penis.length {read and write} - Controls his penis length. Values range from 0.7 to 1.2 normally, but with mods this can change. See minSize and maxSize variables.
da.him.body.penis.width {read and write} - Controls his penis width. Values range from 0.7 to 1.2 normally, but with mods this can change. See minSize and maxSize variables.
da.him.body.penis.minSize {read only} - Retrieves his min penis size. Useful in combination with penisrange mod.
da.him.body.penis.maxSize {read only} - Retrieves his max penis size. Useful in combination with penisrange mod.

You can color the following body components with r,g,b,a. RGB values go from 0 to 255 and the alpha (a) goes from 0 to 1.
da.her.body.iris.<colorComponent> {read and write} - For coloring her iris.
da.her.body.sclera.<colorComponent> {read and write} - For coloring her sclera.
da.her.body.eyeshadow.<colorComponent> {read and write} - For coloring her eyeshadow.
da.her.body.lipstick.<colorComponent> {read and write} - For coloring her lipstick.
da.her.body.eyebrow.outline.<colorComponent> {read and write} - For coloring her eyebrow outline, I think. Not sure.
da.her.body.eyebrow.fill.<colorComponent> {read and write} - For coloring her eyebrow fill color.
da.her.body.blush.<colorComponent> {read and write} - For coloring her facial blush.
da.her.body.mascara.<colorComponent> {read and write} - For coloring her mascara.
da.her.body.freckles.<colorComponent> {read and write} - For coloring her freckles.
da.her.body.nailpolish.<colorComponent> {read and write} - For coloring her nailpolish.

You can color the following body components with h,s,l,c. The hue goes from -180 to 180 and SLC values go from 0 to 4.
da.her.body.skin.<colorComponent> {read and write} - For coloring her skin.
da.her.body.hair.<colorComponent> {read and write} - For coloring her hair.
da.him.body.skin.<colorComponent> {read and write} - For coloring his skin.

For a full listing of all variables exposed by DialogueActions and add-ons for DialogueActions, you can go to the Custom tab of the ingame menu, Edit Dialogue section, and view the dialogue log.
The dialogue log will mention what variable setters and getters are registered.

For clothes, clothingType (Loader mod clothing may use different amounts of values, which is why DA supports 8 RGBA for all)
[panties]   3 RGB values
[bottoms] (her pants)  6 RGB values
[legwear]   8 RGBA values
[legwearB]   8 RGBA values
[footwear]   6 RGB values
[top]  (her bra)  3 RGB values
[tops]  (her shirt) 4 RGBA values
[armwear]   3 RGB values
[eyewear]   3 RGB values
[headwear]   6 RGB values
[tonguePiercing]  3 RGB values
[nipplePiercing]  3 RGB values
[bellyPiercing]   3 RGB values
[earring]   3 RGB values
[collar]   6 RGB values
[cuffs]    6 RGB values
[ankleCuffs]   6 RGB values
[gag]    3 RGB values
[himTop] 3 RGB values, male body only
[himBottoms] 3 RGB values, male body only
[himFootwear] 3 RGB values