You guys want to put together mixtapes, but in a little different format? We pick a broad "theme", set up an e-mail address and then everyone sends their songs to that e-mail address. The first 15 or so make the cut, then we move on to the next "theme" as picked somehow. The songs are compiled and uploaded on sendspace or some other file hosting site in the order received.
I've tried this format on another website I frequent and it works out pretty well. You can also get a wide variety of songs if you make the theme very broad and open to interpretation.
Would you guys be interested? If so, an interesting theme to start with might be "Songs that build"