Good music apps for Ipod/Iphone?

Any good apps for music? Something like 4shared would be great. I want to be able to look up a song, download it, then be able to listen to it with or without internet connection. Any suggestions would be apreciated!

Spotify. You have to make an account in Safari before downloading the app. Go to Safari on your iDevice and type in https://www.spotify.com/us/signup/ in the bar where you type in links. Make your account. Close out then download app. After that log in and enjoy.