I think I may have posted on this a while back when it was only an idea, but it has now come to fruition. Derek Webb, solo artist and former member of Caedmon's Call came up with the idea and implemented it a while back by giving away a free album as a download if you give him some of your information (email, zip code and three email addresses of friends). He used that information to find fan bases so he could plan his venues based on known fans who would come and support him. So basically he traded his music knowing that giving that away to his listener base would pay off at his shows; plus it allowed for others who would not spend the money to sample his music to do so risk free and he could gain another potential fan.
Since that time he has made a website and opened it up to other artists to share their work in the same way. He also gives you the choice to purchase the music at a price you set if you are not comfortable giving him (or the artist) your information.
So go check it out (you can listen to every song on the site for free to see if you are interested in it and if it would appeal to your friends).
The site is called NoiseTrade.