Auctioneer - Go for the Auctioneer Classic AFAIK its a stable release, Auctioneer Advanced is still not 100% though.
GarbageFu/GarbageFu Prices - Can poll Auctioneer for prices, but isn't a right lot of good if you don't run FuBar.
Loot Filter - Is good at filtering what you actually pick up and keep, less good the more complicated the sorting you want to do, and with really complicated lists it does lag. It also opens things (eg clams) and auto loots them which really makes a difference when fighting Naga & Murlocs.

Personally I run all three (and a ton of other stuff) and have few issues.