WowAce

mount and companion manager

Provides one or many informational windows with optional interactive widgets.

SacredBuff

Create panels for customizing your UI, sucessor to eePanels

Prat

Tracks vulnerability debuffs on multiple mobs

Auto repair + shows durability.

Adds various information based on PeriodicTable to item tooltips.

Rebuff yourself with the mousewheel.

Tracks the HoTs you cast.

Am I locked out? - Displays all RaidIDs for all chars

Configurable Castbars

Database of Diminishing return categories and general data

Detox

DaHud

Display auras on action buttons.

Archaeology Assistant

Queing of /who and SendWho() queries and a much better interface (see docs), with gurantee to be executed & callback.

A fancy LDB reputation display, show faction reputation and reputation change history

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