I posted earlier about the Future of Muslim Music and looks like I was a little behind. 
The Brotherz are a Muslim Acapella group who make the Naturally 7 I posted before look like amateurs.
Check out these links to listen to their halaal (non-instrumental) music. Again this follows the opinion that beat-boxing and sounds generated by the human voice are halaal.
Enjoy!
Subhana kallahumma wa bihamdikha ash-haduana la illaha illa ant astaghfiruka wa atubu ilayk. Ameen.
