WowAce

In-game theorycraft. Calculates actual damage/healing based on gear, talents and buffs.

Co-ordinated targetless Party and Raid wipe recovery. Evolved

Displays your soulshards in better way.

Speeds up triggering actions such as items or spells by triggering them on key/mouse down rather than release

ControlFreak

Buff reminders and more

Target Debuff monitor. Stacking aware, giving current and potential debuff status.

End of combat reporting for feedback on how your cast time was spent or wasted.

Mana regen rate display.

Experiments in Mana/Regen Tracking

Manaburn

FuBar_MageFu

Out of Mana bar.

Simple addon that tracks internal cooldowns.

Templar is the ultimate Mage Assistant

Displays a graph of the player's Mana regeneration

Addon for knowing exactly when you get out of combat so that you can drink.

OrbMaster