WowAce

Keeps track of durability and pops up a dialog to repair when you go to a vendor who can.

LDB display of currencies, gold totals and session / daily / weekly statistics for all characters on a server.

Keeps track of performance of memory, latency, and framerate.

Achievements

Incoming Heals

MendWatch

Shows Status Bars that you can drag around and group up for your cooldowns

Display Garrison missons for all Characters

Tracks the Blood Shield for Death Knights.

Static library of wow map data

Does stuff for sachmo

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

Shows where the equipment of inspected users or yourself is from.

A library for PvP and Battlegrounds

Provides quick access to information on your group and their equipment, enchant and gem choices.

Compact rune and proc display for Death Knights.

Detox

FuBar_AnkhTimerFu

Provide plenty of links

Mutes various chat related annoyances while in capital cities and instances.