QuestHelper tells you how to finish your quests in the easiest, fastest manner. It includes a database of quests, monsters, and items, telling you the exact location of that dang Perfect Satyr Horn you cannot find.
It also computes the fastest path to complete all your quests and gain experience - as quickly as possible.
It currently survives on donations. Anything you can contribute is appreciated. QuestHelper makes your $15/month World of Warcraft subscription more enjoyable, and only a few dollars a month ensures that will running forever.