http://vgmq.garoux.net/
Here's a neat little site I found. It's got about 300 songs from random games. Each song is rated on a point scale of 1 to 10 where 1 is the easiest. You do have to sign up for an account, but it just asks for your email address. You only get 1 guess, so don't waste it. It'll tell you if you're correct, but if you're not, it'll either say incorrect or "Your answer is pending."
At about 3 point songs, the songs start getting pretty hard. Even some of the 2 point ones I couldn't make a guess. So far, me and a couple of my friends got a total of 117 points at about halfway through.
Good luck!