Today I discovered Muxtape which is a quick way to throw together a mix tape of sorts by uploading MP3s to their website. Anyone can then go to your Muxtape page and listen.
Not sure about the legality of this one since they're storing unpaid for music on their server and letting others listen at no charge.
At the least, it's a good way for the site owners to build a massive MP3 collection of their own.
I posted two songs today on my Muxtape.