Soundcloud.com is a great online track sharing service definitely worth a look... I participated as a beta tester, but am in no way affiliated with the company. Just posted an update & video of the service description
on my blog for further info.
The first question that comes to mind is what's the benefit above and beyond email and/or FTP (especially since the pro options can appear expensive at first glance)? In my opinion, this is vastly superior approach; it's faster and more secure, but mostly it's the collaboration tools that won me over.