This site has gone south, folks. The previous owners sold out to corporate music. It's no longer indie-friendly. DO NOT BOTHER GOING THERE. It now hosts major label bands. Independat artists are no longer there.
The only good thing to come out of that transaction was that I found Soundclick.
This site is the best reason to have internet access. It is the best way to find and hear new and up-and-coming musical artists that there is. IMO, it is the 21st century replacement for the radio as a source of new music. It also has the best search engine for musical styles that I have found. You can search for specific musical genres broken down to many sub-levels (some I've never heard of) or you can enter a favorite artist and search for artists that have a similar sound or were influenced by that artist. There are TONS of free MP3's in every musical style you can imagine, as well as streaming audio. Best of all, it's free and legal!
This site is a good overall MP3 site it deals with mainly independant artists but there are a few popular artists there also. Some of the music is free and downloadable, some requires purchasing to get the full bit.