The popular tactic for pally tanking after level 75 seems to be this "696969" thing. The basic idea is that you have three spells that have 8 or 9 second cooldowns and two spells that have 6 second cooldowns:

9 ( or 8 ) second cooldowns:
Holy Shield
Consecration
Judgement (After spending one talent point.)

6 second cooldowns:
Hammer of the Righteous
Shield of Righteousness

If you alternate between 9 second cooldowns and 6 second cooldowns, you can make sure that you make use of every single global cooldown. My hope is to have this all consolidated into one spammable macro. So far I have a macro that will work if you press it once every 1.5 seconds. Here's that macro:

#showtooltip
/console Sound_EnableSFX 0
/castsequence [nocombat] reset=5/combat/target seal of vengeance,Avenger's Shield
/castsequence reset=combat Holy Shield,,Consecration,,Judgement of Wisdom,
/castsequence reset=combat ,Hammer of the Righteous,,Shield of Righteousness
/console Sound_EnableSFX 1

Edit: For needed clarity, the important part of this macro is the fact that it uses double commas to offset two castsequences, essentially jumping back and forth from the first in-combat castsequence to the second.

The lines about sound enable are to get rid of that irritating "BWANG!" sound that you get from spamming a button for a spell that's not ready yet. The nocombat line is for pulling.

The problem with this macro is that it is not spammable. This macro will only work if you press it once every 1.5 seconds. I would like to have a single button that I can spam for my mage dps and my pally tanking. The mage's spells should be ready at 1.5 second intervals, though, so perhaps I could get away with just pushing that button once every 1.5 seconds. I'm still a little worried that the button might get pushed too soon for one of the two chars, leaving him standing there doing nothing for a full global cooldown.