Edit: Fixed the pally macro.

I think I've finally perfected my macros for my 3box team, so I figured I'd share them.

Note: My pally's name is Adiabat. When the macros refer to "Adiabat", this is where the pally's name goes.

Pally:

Bind the following macro to keys 2 and 3:

/console Sound_EnableSFX 0
/castsequence [nocombat] reset=5/combat/target seal of righteousness,Avenger's Shield
/castsequence reset=10/combat ,holy shield,judgement of wisdom, consecration
/console Sound_EnableSFX 1
/script UIErrorsFrame:Clear();

Mage:

Bind the following macro to key 2:

/cast Combustion
/use 14
/castsequence [exists,harm,nodead] reset=12/target fireball,scorch,scorch,pyroblast
/stopmacro [exists,harm,nodead]
/assist Adiabat
/cast [nocombat] pyroblast
/castsequence reset=12/target fireball

Bind the following macro to key 3:

#showtooltip scorch
/cast scorch
/stopmacro [exists,harm,nodead]
/assist Adiabat
/cast scorch

Priest:

Bind the following macro to key shift+2:

/use14
/castsequence [exists,harm,nodead] reset=24/target Holy Fire,devouring plague,shadow word: pain,smite,smite,holy fire,smite,smite,smite,smite
/cast [nocombat,target=adiabat] Power Word: Shield
/stopmacro [exists,harm,nodead]
/assist Adiabat

Bind the following macro to key shift+3:

#showtooltip Smite
/castsequence [exists,harm,nodead] reset=8 Mind Blast,Smite,Smite,Smite,Smite
/stopmacro [exists,harm,nodead]
/assist Adiabat
/cast Smite

Bind the following macro to key f2:

#showtooltip
/cast [modifier:shift, target=Isochor] [modifier:ctrl, target=Isobar] [target=Adiabat] Greater Heal

Bind the following macro to key f3:

#showtooltip
/cast [modifier:shift, target=Isochor] [modifier:ctrl, target=Isobar] [target=Adiabat] Renew

What this does:

To pull, target something with the pally. The priest and mage should not have hostile, living targets at this time. Hold shift and press 2 once. The pally casts seal of righteousness, the priest bubbles the pally, and the mage begins to wind up a pyroblast. If combustion is ready, the mage will also toss up combustion. The priest and mage will both use their trinkets if they're ready. Press shift+2 a second time right before pyroblast finishes. The pally will pull the target with Avenger's Shield and the priest will start her dps rotation with Holy Fire. Spam shift+2 until the target is about 5 seconds away from death.

Once the target is near death, spam shift+3 instead. At any point after the initial pull, the pally can switch targets to build up threat on the next target and the clothies will continue attacking the first target.

If the priest needs to stop dpsing, release shift. Spamming just 2 or 3 without shift pressed will cause just the pally and mage to do their things. The healing macros are pretty self explanatory.

Features to note:
The pally macro includes a script that makes it so that the macro doesn't display error messages or make that irritating sound while you're spamming it. This script turns itself off at the end of the macro, so other spells and stuff still display error messages.

Combustion is not on global cooldown, so it can be in the macro and allow the rest of the macro to still function.

The order of the [nocombat] parts of the priest and mage macros is very important. It's hard to explain the logic behind them, but basically the mage only opens on a fresh target with pyro if he's not in combat; otherwise he opens on fresh targets with fireball. The priest only tosses up pw:s if she's out of combat; once she's in combat the dps macros will only cause her to dps.