Easy: From Ironic Sans, see how many US States you can name in ten minutes. I got all 50 in 3:23.
Hard: The Impossible Quiz Deluxe from DeviantArt (takes a while to load).
Potentially Addictive: Vox Imperium, a web-based civilization-type game. I haven’t tried it yet. I’m not sure if I should but here are instructions how to start.