Project Euler

I recently discovered an awesome site, projecteuler.net, which has 202 mathematically-based programming tests. This is really helpful to someone like me who's learning a language and needs some practice, but doesn't have to program for his or her job. You can download my solution to problem three, in python, (preferably after you've solved it yourself) at tauntaun.10gbfreehost.com/code/problem3.zip
If you know of any other similar sites that supply programming challenges, I'd love to hear about them in the comments. Unfortunately, I have a sneaking suspicion that no one but me will ever see this post.
I've also tried the quizzes at pythonchallenge.org, but those seem to move at a much faster rate and, well, I'm a little slow.