http://www.youtube.com/watch?v=PZu3FROFXqk Amazing jazz track. I wouldn't say it's unknown but it's far from mainstream.
http://www.youtube.com/watch?v=VUWmuZ3WvWw Depending on what you're into you might already be familiar with this but it can never get enough exposure IMO. Heavily influenced by Danny Elfman.
http://www.youtube.com/watch?v=1I_Ob3HELcY I don't think the soundtrack for this is even available but the music in this game is amazing. I love this fight music in particular.