Well here is something I discovered not a long time ago: the music genome project. Basically this is a streaming music "station" on the web where you input song and group you like and they make you listen to songs they think you will like based on the musical quality of the song you inputed. Their selection of song is rather limited (they don't know Symphony X for exemple and I couldn't find any classical artist.) but they still manage to show me a group or two that I had never hear of and that fit right into my taste of music.
So I'd advice you to check it out and see if it work for you, to correctly check it you have to perform a small internet trick but I will not give you more details then that.