Bridge, Gremlin, Music2iPod. I've tried all 3 of these on iOS 6. Not sure if they're updated for 7.x yet though. Bridge is a paid app while the others are free. And like the other poster said, mewseek is another one. I've never used that one though but I'm sure it's fine if it works on 7.x. Mewseek allows you to search and download music. It's a paid app too. Kinda expensive if I remember correctly.