The
Hype Machine is pretty good for discovering new music. It's led me to some good blogs in the past where there's a host of great MP3's to download (for free)
I also scrobble all my music to
last.fm and that site will come up with some pretty good recommendations based on your listening habits. You can listen to loads of tracks there too for free as you also can on
Spotify
I used to get some great recommendations here but the headset forum is something of a ghost town these days. I use other forums and also sites like Pitchfork, Drowned in Sound, Resident Advisor, DJ History etc