May I suggest http://soma.fm and their streams, also Pandora and it's related artists. Both services can be tricked into saving songs if you need to. Also, last.fm has some reasonable stuff, like Pandora, related. There was even an segment in one of the episodes about Spotify, same deal.
I work best to 65daysofstatic, Mogwai, Explosions In The Sky and other mathrock and vocalless electronica. There's plenty of free and "free" music out there, but don't do drugs, stay in school and buy the album.