I just took a whole load of short guitar riffs and posted em at PrimeTones for cell phone users to buy as ringtones.
...don't have have a clue what Ringtones actually are or if they'll bring in any cash but hey...
I saw an article for them in Canadian Musician & looked through the legalities pretty thoroughly so they look legit.
Basically all ya do is take your guitar riffs, (or songs) and upload them there as MP3's. They advertise for you and do all the maintenance for free. If you sell anything they give you a 20% royalty. (kinda low but you keep the copyright and all ownership of your material)
For stuff 29 seconds and under they sell em as Ringtones for cellphones.
For full length MP3's and songs, you pick whatever price you want to sell them.
I don't know if I'd wanna sell ALL my songs there, but for short little riffs that are sitting around doing nothing, if it promotes your name and maybe pays for a few beers, what the hell.