8tracks is a website where people have playlists that you can listen to for free. You can also become a member.
I think it is a really cool website. You can find a playlist to fit whatever mood you are in, and if you find someone whos playlists you enjoy then you can follow them, like you do on Twitter.
Some that I am currently exploring are:
and my roommate/best friend and I watch How I Met Your Mother primetime on CBS or reruns on Lifetime and in one episode Barney has a playlist and this is it!