WowAce

Displays bars depending on your professions

Tracks and announces interrupts (eg. Hit/Miss/Immune) and is also able to track and report "wasted" interrupts (those which d...

Handles the assignment, coordination, and announcement of many parts of the Lich King encounter in Icecrown Citadel.

Does a /who search of multiple dungeons.

BossWhisperer

A popup menu containing user-programmable scripts.

Adds your damage to Scrolling Combat Text

HealComm-2.0

A simple addon that warns you if your pet isn't attacking while you're in combat.

AnchorsAway

ImprovedTargetFrame

tekProber

Shows loot information in item tooltips

Simple Bars for your Shaman's weapon buffs and shield spells.

A library to help with localization of Archaeology artifacts

Library to help with querying unit talents.

Cryolysis

Shows you which bosses you've killed next to the raid finder frame.

Capsule

Reverse Engineering will drill down and search your tradeskills for their elements