Addons:

WowAce - Home of such addons as AutoBar, Omen, Recount, Grid, Cartographer, FuBar, ClosetGnome, OneBag and TradeskillInfo. Comes with an optional auto-updater.

WowInterface - Home of many addons and a distribution point for many others such as Bongos.

CTMod - Home of the various CTMod addons, to include CTRaidAssist.

DeadlyBossMods - Home to Deadly Boss Mods, a useful collection of boss fight timers.

Curse Gaming - Home to many addons, including ImmersionRP. Also includes an optional auto-updater.

Auctioneer - Home of Auctioneer, Enchantrix and Gatherer.

GEM 3 - Home of the Guild Event Manager addon.