TourGuide has to be one of the best WoW addons I have seen. As far as power leveling goes it is extremely useful. Not only does it work well out of the box, but you can create your own guides with it. The default “tour” works fine, but I have noticed that I am not the only person running the same quest circuit. So in time, you’ll need to use an alternative guide for it.
Essentially, TourGuide leads you through a predetermined sets of quests and areas in a highly optimised way. Once you have this addon installed, you will see a small quest indicator, that will tell you where to go, what quest to pick up and what to do them. The notes are sparse so sometimes you will have to figure out how to compete a quest if you don’t already know it. If you use this with QuestHelper, you’ll have everything you need to power level through most of the game.
I’ll put up some screenshots explain this addon further. For now, follow the link above and enjoy.