Here are some links that hopefully will be of some 
use...http://www.nmpa.org/
http://www.ascap.com/ascap.html
http://www.bmi.com/home.html
http://www.umusicpub.com/index.html
The first one is for the Harry Fox agency which is probably 
one of the best online licensing agencies.

http://www.kohnmusic.com/ (Very good site!)