Yeah, fun time. It technically is legal. You can sell anything that can be legal defined as goods or a service exchange for money on the Internet. It is all a matter of finding someone brave enough to buy it from you.
http://buymysoul.net/ Charity Group that barter's souls to help people....hopefully.
There was also a site on the Internet where you could buy, trade, and sell souls as a form of a weird game. It was like trading up through Craig's list, but done completely with your soul. You would trade people ideas, web site addresses, or whatever they wanted for control of their soul on the site. I don't remember the name though, just that I know someone who participates in it.
Buy,Sell, and Trade ideas:
http://www.newideatrade.com/
If you create your own song, I know their are avenues to sell and buy DRM free music through iTunes, Amazon, and 7digital.com.
can someone shed me some lights on how copyrights of song can be transferred? thank you
P.S. The copyright to anything can be bought and sold. Hell the legal ownership of every Beatles song was famous bought by Michael Jackson in a public auction pissing off his close person friend John McCarthy. Mr. McCarthy has control of them now I think.