Next time you find yourself belting along to Cyndi Lauper singing "Girls Just Wanna Have Fun" or Joan Jett singing "I Love Rock 'n' Roll," know this: Cyndi and Joan didn't originate those songs, they just made them famous. Huffington Post rounds up 20 hit songs that are actually covers. Check out a sampling in the gallery of both the originals and the covers, or click for the full list. (More celebrity stories.)