I run a 3-box, Tank, Healer and DPS.

My healer is a 66 Holy Pally and his setup is 4 buttons:
Key U: /cast [target=Party1] Holy Light
Key I: /cast [target=Player] Holy Light
Key O: /cast [target=Party2] Holy Light
Key P: /cast [target=Party1Target] Holy Shock

U heals the tank, I heals himself, O heals the DPS. P heals or hurts the tank's current target.

If I want to use Flash of Light, I use Shift+Key for U, I and O.
From there, I do other macro for Alt+ and Ctrl+ using Divine Favor in the Holy Tree + Spell