I didn't go back and read the whole thread, but I don't remember anyone talking about add-ons they use. Here's a few I've found to be helpful:
CTMod: I got the advanced pack and probably don't use most of the features. Best things it does is give you map coordinates so you can get to quests easier. It'll also tell you what level the quests in your log are. Like I said, does a BUNCH of other stuff as well.
QuestHelper: looks at all the quests you have in your log, then determines the best order you should follow to complete them and gives you directions on your map on where to go. Very helpful for levelling!
Auctioneer: download the preview version from this link. Another set of tools which helps you use the auction house more efficiently. You can use it to scan the AH to see what things sell for. Once you build up enough information it'll suggest appropriate prices for you to sell things. You can also use it to scan for bargains which you can turn around and re-sell, but I'd wait until you have a better feel for what things will actually sell for (Auctioneer ain't perfect!) before you start doing this.
And if you don't know about
Thottbot and
Allakhazam, well, check them out right away.