you can listen to *every* song, even whole albums before you buy it. But you don't have to buy anything at all. They think, if you like the artist's music you will buy the album and, since about 50% of the revenue go directly to the artist, support him/her.
I found some very good tunes there; and a recent checked confirmed that all kinds of genres are served. It's not really DonationMusic.com or DonationArt.com but you get the mp3 for free without any restrictions whatsoever and if you like you can buy stuff. People are even encouraged to spread the mp3s.
Since I am not always sure what genre other people like, I rather spread the URL
There are more labels like this one. One, specialized in drum'n'bass, is Exegene
. I am convinced when you look around you will find a lot of good free music for just about any genre. Like there at least two internet radio stations for every genre you can dream of, even whale songs