Macros and Add-Ons

Bayn's World of Warcraft Mods and Macros
Macros to call for assistance and to quickly switch weapons.
http://home.austin.rr.com/adepts/

Curse Gaming
A large database of add-ons for the World of Warcraft client to enhance game play.
http://wow-en.curse-gaming.com/downloads/addons/

Wobbleworks Warcraft
Official addons site for Group Calendar, Outfitter and other addons written by John Stephen.
http://wobbleworks.com/warcraft/

WorldofWarcraftMods.org
Contains a comprehensive database of World of Warcraft mods all available for free to the community with no registration required.
http://www.worldofwarcraftmods.org/

WoW Macros
Presents a collection of macros organized by character class.
http://wowmacros.com/

WowAce
Offers add-ons based on a common library set as well as an adware updater and installation tool for all offered add-ons.
http://wowace.com/

WoWInterface
Offers interfaces, skins, add-ons, mods, and a community.
http://www.wowinterface.com/