I've heard about ProjectEuler.net over a year ago and it quickly slipped my mind. Last week I rediscovered the site and finally registered with them. Project Euler (according to Wikipedia, pronounced "Oiler") is a site of over 300 mathematical problems with the intent of them being solved through creating an efficient algorithm and programming it out to get the result, read their about section here. Once you register, it'll keep track of which questions you've completed and what the answers for those problems were. Upon completing a problem, you can also access a forum thread about that problem. There, you can see how other people solved the problem. Usually other users will post their code or explain their approaches.
I have created a solution in Visual Studio that all my projects for every problem is going into and I'm taking on the challange of getting as many done as possible. At this time of posting, there's 311 problems and I've completed the first 18. I'm slowly working my way through them and I'll keep you all posted. They're constantly adding new problems so reaching 100% will be short lived if it happens.
I highly recommend this site to developers looking to stay on their mathematical game or mathematicians who are looking to learn how to program. Regardless which you are, you're going to better learn to develop algorithms. I know I've learned quite a few ways to interact with numbers. The biggest surprise for me was how to count the number of divisors a number has when you know it's prime factors. Anyway, have fun with this site.
Advice, Code Optimization, Misc