WowAce

Tracks vulnerability debuffs on multiple mobs

Additional information about player spells.

CT_RaidAssist style raid frames

Rebuff yourself with the mousewheel.

Checks your gear before bosses and yells at you if you're an idiot

Reports in raid chat whenever a raid member "fails." /EnsidiaFails to configure.

Display aura information inside action buttons

Tracks the HoTs you cast.

Barks at you when you target a crowd-controlled unit

Test whether the player can really dispell a buff or debuff, given its talents.

Shows you the radius of your totems.

Compact & customizable filtering, monitoring and grouping of buffs and debuffs

Attach diminishing return icons to unit frames.

A collection of Rogue modules.

Modular and lightweight party/raid frames.

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

Tracks the Blood Shield for Death Knights.

Tracks the current Fear Ward's in the raid or party.

Personal buff monitor - are you buff enough?

Keeps track of HoTs, DoTs, Buffs and Cooldowns. With audio and text alerts to refresh them.