Pandora:
By now if you don't know what Pandora is its probably not for you, anyways its internet radio the way it should be, you choose an artist you like and it starts playing similar music for free over the internet, you pick which songs you like and which ones you don't and it starts learning your kind of music. Its fantastic!

The only problem its its not available for T-Mobile yet, only Verizon, Sprint and AT&T