Are you using them?
Grab the Curse client from
http://www.curse.com/ , it does all the updating for you
Auction Stats - scans the auction house and saves price data
Branderic's letter opener - takes items from letters, the 'proper' way of doing it is very slow
Curse Profiler - gathers in-game data to refine the Curse database
Fast Friends - Updates your friends list across your alts
LibSlash - Dev tool, needed to run some of the other add ons
NPC Item sale Price - imaginatively titled tells you how much you can vendor stuff for
PassCraftMats - auto passes on craft loot (disable if you're a cultivator)
Rolodex - Offers a list of your Alts and guildies when mailing stuff
SendStuff - allows bulk mailing without tripping the posting limit. Handy for gathering Alts