Here's the short list.
_NPCScan Tracks seldom-seen rare mobs by proximity alone.
AI-Art Reskins almost all of the default blizzard frames. Also has skins for Auctionator, WIM, and in game icons (Seperate downloads).
Advanced TradeSkill Window ATSW is a complete replacement for Blizzards tradeskill window with more overview and special functions.
Auctionator Auctionator is an easy-to-use but powerful World of Warcraft add-on that helps you buy, sell and manage auctions.
Bazooka Bazooka is a Data Broker Display similar in functionality and looks to FuBar.
Broker_Currency LDB display of currencies and gold totals for session / today / yesterday / this week / last week.
Broker_MicroMenu Shows the micro menu and game menu in a clickable broker tooltip. Also shows your fps and latency.
ButtonFacade ButtonFacade, with its associated library, is a small add-on that allows for the dynamic skinning of button-based add-ons.
ButtonFacade: Aion This is a skin for ButtonFacade
Combuctor Combuctor is a bag replacement addon designed to help the player find things in his or her's inventory as quickly and as easily as possible.
DocsUI Nameplates Changes name plates and unit frames to show more info.
GupPet GupPet is an add-on that gives an extension for mounting and calling critters.
HandyNotes Handy Notes for your maps. This addon is intended to be a small and simple replacement for Cartographer_Notes and functions in a similar manner.
LightHeaded LightHeaded is a very simple addon that displays quest information and comments from
http://www.wowhead.com in game.
LilSparkys Workshop LilSparky's Workshop adds auction-derived pricing information for trade skills right into the trade skill recipe frame
Mapster Mapster is a very simple world map enhacement addon, which was designed to work in conjunction with all other map addons out there.
nibSpellAlertConfig nibSpellAlertConfig allows you to configure basic settings (size, position, etc) of Cataclysm's new built-in Spell Alerts.
nUI Industrial Dashboard art
nUI Integration ButtonFacade Skin nUI buttons with ButtonFacade.
Parrot Displays Events from the combatlog (damage, healing, ...) as moving text and numbers across the Screen.
PhanxChat PhanxChat removes chat frame clutter and adds some functionality.
Raven Customizable timer bar and icon configurations to monitor buffs, debuffs and cooldowns
Skada Skada is a modular damage meter with various viewing modes.
TomTom TomTom is your personal navigation assistant in World of Warcraft.
WIM WIM is a World of Warcraft addon which helps you to manage your whispers by making them into a classic instant messenger interface such as AIM, Yahoo and MSN.
WoW Pro Leveling made easy using tourguide.
ZOMGBuffs All in one buffing mod for all classes, overview of important raid buffs and instant access rebuff on right click.