There are a lot of places to find macros, but I felt it might be helpful for some to have a compiled list. These are some of the macros I use. I hope others will list their macros in an effort to have a good source of information. I use mostly mouseover macros to heal as they work well with Grid.
http://www.wowwiki.com/Making_a_macro is a great site if you are not familiar with macros and it’s a nice read.
Layout of this thread will be: Actual Macro followed by a brief description of the macro.
/cast [button:2] Prayer of Fortitude; Power Word: Fortitude
This macro allows for left click Power Word: Fortitude and right clicking it will cast Prayer of Fortitude. Also works for Divine Spirit and Shadow Protection.
/cast [harm] Holy Fire; [target=targettarget, harm] Holy Fire
This macro will cast Holy Fire like normal if targeting an enemy, but if targeting a friendly target it will cast Holy Fire on your targets target (providing it’s hostile). Great for healers in Arenas especially 2s and also for throwing some extra dps while targeting MT. Works for other offensive spells also.
/cast [target=focus] Shackle Undead
This macro clears focus then sets your target to focus. It then casts Shackle Undead on your focus. It reshackles the target until its dead or you hold down alt and cast it.
/cast [target=focus, exists] [target=mouseover, harm]  [target=targettarget, harm] Mana Burn
This Mana Burns in the following order: Focus, mouseover, target, target of target.
/use Conjured Mana Strudel
/use Honeymint Tea
/use Star's Sorrow
Drinks water in the following order: Mana Strudel, Honeymint Tea, Kungaloosh, then Star’s Sorrow. This will always drink Star’s Sorrow in Arena.
/cast [nomodifier:alt,target=mouseover,nodead,help][nomodifier:alt,help,nodead][nomodifier:alt,target=targettarget,nodead,help][nomodifier:alt,target=player][modifier:alt,target=player] Flash Heal
This casts Flash Heal in the following order: mouseover, target, targets target, self. Holding alt will always cast it on you.
/cast [target=mouseover,nodead,help][target=target, nodead,help] Renew
/cast [target=mouseover,nodead,harm][target=target,nodead,harm] Shadow Word: Pain
This casts Renew on a friendly mouseover first, then friendly target if you have no mouseover. If mouseover is hostile it casts SW:P on them, if you have no mouseover and your target is hostile it casts SW:P on them
/cast [nopet,harm][nopet,target=targettarget,harm] Shadowfiend
Casts Shadowfiend on Target if hostile, if target if friendly then it casts it on targets target. I mainly use it on boss fights while keeping tank targeted.
#showtooltip Speckled Tastyfish
For tracking speckled tastyfish in the fishing tournament.
/cast [target=player] Levitate
Dismounts and immediately casts Levitate on you. Great for areal kills.
/cast Mind Sear
Won’t clip Mind Sear while you’re casting it.
/say Resurrecting %t
Resurrects your target and announces it.
/use Spirit-World Glass
/cast Inner Focus
Use Spirit-World Glass then cast Inner Focus
/cast !Mass Dispel
Keeps the Green targeting circle when spamming mass dispel.
/cast [target=mouseover,exists,nodead] Penance
Mouseover Penance if you have mouseover, if not casts it like normal. Also what I use for dispel.
I hope these macros help some people out and hopefully others will add to the list.
All relevant macros are welcome.
*edit* added penance/dispel mouseover macro