For the last three or so years I've been giving away music via various websites Myspace, ReverbNation, facebook etc Sometimes in exchange for an email address, sometimes not.
Yesterday I put my album up on Bandcamp and posted some links on Twitter, facebook and myspace. Bandcamp is great - really high quality downloads - MP3 apple lossless ect. The deal was a Radiohead style "pay what you want". The response has been really good, lots of downloads and the amazing thing is people will still pay. They want to pay for music and support the making of new music(I'm defiantly not into profit at the moment). Even better some people have spread the word via facebook and myspace. Restores your faith in humanity.