awesome and fairly complete music genre lists:

rock:
http://www.allmusicguide.com/cg/amg.dll?p=amg&sql=73:20

jazz:
http://www.allmusicguide.com/cg/amg....amg&sql=73:196

electronica:
http://www.allmusicguide.com/cg/amg....g&sql=73:11605

and the lists go on!