One of the best decisions Blizzard made when programming World of Warcraft was to open the user interface (UI) to allow players to create custom modules that can display various information about the world in new and creative ways.
World of Warcraft add ons let anyone with a little programming knowledge remake the interface of the game into their vision of what it should be and allow the rest of us easy access to tons of great information that wouldn’t otherwise be as easily available.
First, just in case you’re worried about violating the WoW terms of service for using add-ons, let me assure you that Blizzard has absolutely no problem with players using them. They won’t help you troubleshoot problems with add-ons should you install one that doesn’t work right but you’re free to use as many as you want to!
Here’s a top ten list of what I’ve found to be the most useful WoW add-ons:
Notice that this screenshot was taken before the other items in the backpack were auctioned off. In fact, this character is at the gold limit so these items need to be mailed to another character to auction because he can't hold any more gold.
I can make this kind of gold because I know what to farm, where to farm it, and what to buy and sell at the auction house for maximum profits in minimum time.