The companion site to World of Warcraft Programming, wowprogramming.com is a great resource on the game's API. It includes function lists, widget handlers, listings of CVars and events, etc. It also is home to a FrameXML browser to view the game's Lua and XML code, an artwork browser, a web-based Lua interpreter and a BLP converter. http://wowprogramming.com/
BBEdit and TextWrangler are both from Bare Bones Software. BBEdit is full-featured and has a free-trial, while TextWrangler is its "little brother" and is free to use. http://www.barebones.com/products/
Please feel free to add your own resources to the thread!
"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh