I'd add Lee Hyla and suggest either CD recording of his music that's available. His style is very different from most modern classical, but I also recommend it because I'm a sucker for his use of low reeds.
Also Charlemagne Palestine. Didn't think I liked minimalism until I heard Schlingen Blaengen.
Hmm, I'm a little sad that Harry Partch and Lou Harrison aren't mentioned. But then, they weren't the most influential composers either; no one really paid much attention to them. If you like John Cage, you'll like these guys too.
Lots of others that should probably be added posthumously to that list, too. But my pursuit of the avant-garde is sadly lacking, regardless. I am both sad and excited. So much work to do!
