Wanted to add a couple and put in a few fixes. All of these work with 3.1 as well:
Carbonite Quest is no longer around, it is now the full Carbonite.
Link: Carbonite : WoWInterface Downloads : Carbonite
AutoProfitX is a great addon that is a one click press to sell the grey items in your inventory:
Link: AutoProfitX - Addons - Curse
AutoRepair is very handy since many people, including myself, sometimes forget to repair. It will automatically repair your gear when you visit a vendor that can do so.
Link: AutoRepair - Addons - Curse
Fishing Buddy is a bery handy fishing addon that does many things. Tracks what fish you've caught from where, stores a fishing outfit, keeps track of the Fishing Extravaganza timer as many other things.
Link - Curse:Fishing Buddy - Addons - Curse
Link - WI: Fishing Buddy : WoWInterface Downloads : TradeSkill Mods
Collect Me is a great addon for those collecting pets and/or mounts for the achievements. It has an easy to access window, 3d view of *some* pets and will tell you where to get them and their price.
Link: Collect Me - Addons - Curse
Wintergrasper Advanced is the last one I'll mention. It simply keeps track of the timer on Wintergrasp as well as makes it easy to post the time in chat.
Link - Curse: Wintergrasper Advanced - Addons - Curse
Link - WI: Wintergrasper Advanced : WoWInterface Downloads : PvP/Arena/BattleGrounds
Just a few that I think many would like if you put up. They're all great addons that work exceedingly well in what they're designed and all updated frequently. Hope some others like these ^_^