Best addons ever:
Atlas -
http://ui.worldofwar.net/ui.php?id=400
and AtlasLoot -
http://ui.worldofwar.net/ui.php?id=2613 (works with a many different types of tooltips, too.)
My other favorite (most useful for paladins) is Group buttons -
http://ui.worldofwar.net/ui.php?id=513
Group buttons provides a bar for you, friendly target, hostile target, party members and a bunch more. Each of these bars corresponds to that person specifically, so you can click on the heal spell in party member #3's bar while targeting someone else and still heal him. You can more these bars around and choose what goes on them. Great for pally buffing and healing.
Example (for priests):
(Though why he has shadow word pain and such on his party bars is beyond me.)