WowAce

Assessment

Provides database of quest giving npcs/mobs/objects for display on the World Map/Minimap

Some handy events that should exist in the default UI

SmartyCatManaBar

Blocks Chinese Chat

Heads-up minimap display

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

Estimated time until current target will die.

Inspects all members of raid and saves in database, as well as lists people's dkp values

Helps you decide which ability to use next according to priority you set

A library to help with localization of Zones.

MorgDKP

AltClick an item in your bag to add it a mail, auction, or trade frame, and alt-click to buy a stack if reagents.

A Simple World of Warcraft Spam Filter!

StatLogicLib

Tankalyze

KoS-Management Tool

Ironi's Encounter Event Tracker

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

LittleTrouble