I don't use a lot of macros with my healing... but if you don't have these, I don't know how you survive ;)
1. /kiss - Because ouchies get kisses. And the macro saves you having to type a whole five letters.
2. /yell Low on mana!
(I know I'm going to get yelled at as a healer - at least this way I can yell back with "Didn't you see me shout I was low on mana?!?" And if that doesn't work - see the first macro)
3. /cast Lay on Hands /yell No! I won't let you die like this %t!
%t inserts the name of your target - and who doesn't want to add a little more drama to their healing? This also works very well with Divine Sacrifice.
And yes... Girly Pally really uses that one. It's mildly embarassing when you target yourself - and REALLY embarassing if you still have the boss targeted from your Judgement of Light. Not that that's ever happened to Girly Pally...
4. /cast Holy Light /cast Holy Light /cast Holy Light /yell STOP STANDING IN THE FIRE YOU IDIOTS!
Because we can only do so much....
5. /cast Hand of Protection /say Saved your butt again %t
Never hurts to to force a little appreciation...
And of course - no discussion of pally macros would be complete without:
6. /use Hearthstone /cast Sacred Shield /laugh
So useful in so many situation! Getting jumped while fishing in Wintergrasp - Hopelessly outnumbered defending that stupid Forge - The raid leader yells "Wipe it!" - Running into your old GM in Stormwind - That 15 year old DK says "Let's dual you n00b"...