I am running a group with a priest, paladin and mage and for buffing I've tried two approaches. One is using the /targetparty function. Each time you run the macro the character will target the next person in the group, apparently using themselves as a start point. So the macros could be:

Priest
/targetparty
/cast Power Word: Fortitude

Mage
/targetparty
/cast Arcane Intellect

Paladin
/targetparty
/cast Blessing of Wisdom


Bind them to the same key (shift-F12 in my case) and just press it X number of times and your group is buffed.

However, I was having some problems with it, it may be that if you take too long between keypresses it resets it or something. It worked fine when I had the mage and priest doing it, but when I added the paladin for some reason it stopped working. Since I run one main character and have the rest work from that character, I did the following. I created a macro to make the party leader the focus of the other characters.

/target party1
/focus


Then I created the following macros and bound them as before:

Priest
/cast [target=focustarget] Power Word: Fortitude

Mage
/cast [target=focustarget] Arcane Intellect

Paladin
/cast [target=focustarget] Blessing of Wisdom

So what I do is select each party member in turn with the mouse, then press shift-F12 and each party member gets buffed in turn.

This won't work for every setup, but since it's primarily a caster group those are the buffs I'd be using the most. My group is also of a low level and being powerleveled by a 70 shaman, so I can be lazy with the focus command... at some point I'll need to add more macros to allow me to recover when the primary character is killed.