I've just discovered Finetune. It struck me today that while I've now got quite a large collection of music on my iPod, covering lots of different musical genres, I'd say 90% of the music is what you'd call commercial from well known artists past and present. I'm often reading reviews of great music on independent labels but very rarely take the time to be adventurous and download something that isn't in the Amazon top 50.
With Finetune, much like LastFM, you can explore playlists that other people have created and listen to them online. There's some great stuff out there and it's definitely encouraging me to broaden my musical horizons!