I originally found this site when I was considering building a site where you'd enter your favorite movies and it'd try to suggest music for you based upon your movie interests. Anyways, I discovered that screentunes actually is an ingenious, unique way of finding new undiscovered music even if thats not what the site is really for. Just pop in some songs, find out what movies they've been in, and then see what other music was in that movie... if one good song is on a soundtrack, chances are they're will be a few others too.
Kudos to screentunes, I have a feeling this will be a big hit soon.