Here are the two main addon clients i use which update automatically with every patch.
Wowmatrix
Curse
For auction house help i recomend Auctioneer Suite & Auction Master along with AHSearch and Auditor/Auditor2 FuBar.
For fast leveling and quest help i recomend Cartographer and Questhelper combined with Lighthead.
For gathering use Gathermate & Gathermate Cartographer import along with Gatherer & Gatherer Wowhead import.

Custom Free World of Warcraft