There's a pretty cool site called imeem.com that according to them is "an online community where millions of fans and artists discover new music, videos, and photos, and share their tastes with friends."
The site not only allows you to build playlists like the one below but you can also set up what they call battles. It's two songs and you can pick which you like better.
Click here to vote on my battle. The question is "Which do you prefer, earlier Beatles or later Beatles?"