WowAce

Reno is a slash-command that can patch predefined options in a macro to change which abilities will be chosen.

New/Old BG indicator, Join by ID, Quick Leave Queue, etc.

RaidSpy

An auction house AddOn to make the life of each fence easier.

RaidInfo

Displays how many times you have jumped.

FuBar_AnkhTimerFu

LDB data source for currency flow

adds navigation buttons to Encounter Journal

Raid loot tracking and text generation

Detects specific CDs and spellcasts

Enables user defined sounds for Party, Guild, Raid and Custom Channel chat messages.

Cryolysis 2

Adds party/raid role icons in useful places

Insanity resource tracker for shadow priests.

Add-on that shows in a unit tooltip window a number of killed mobs of the same kind

A simplistic clock.

This will keep track of how much you have paid per item in your inventory. Only one of (Auctionator, Auctioneer, AuctionLite,...

Pins on the World Map for quests you have not completed yet

Loot management tool