check out this website i ran across today called Loopwise.com Online Music Collaboration Website. http://www.loopwise.com This site is very cool!
here is a copy and paste from their website:
At Loopwise you can register as a Loopwise Studio Musician and offer your services as a musician to the world wide web community, or you can simply post projects and request musical works. If you are seeking help on a current music project of yours, you may post that project here at the Loopwise site for free! Once you post your needs(guitar lines, vocal beds, hip hop beats, etc) along with your MP3, you will get bids in your email from the community of virtual studio musicians here at the Loopwise Site wishing to work with you.
Becoming a Loopwise Studio Musicians has many benefits, including a 10% discount on all orders from the Loopwise.com Store, a portfolio page with up to 10 mp3's, and access to be able to bid on projects posted at the site. As a Loopwise Studio Musician you will be granted access to negotiate with people at the site who need musical works and are willing to pay. This could be a vocalists in seek of a music bed, or an advertiser looking for a music bed for an upcoming commercial. Check the site out today http://www.loopwise.com