Those who haven't heard of or played around on TopCoder don't know what they're missing.

For example, I just spent the last 45 minutes working on a set of three different algorithmic problems. Each rises in difficulty, and you are awarded points based factors such as the amount of time it takes you to finish. There's a set of test suites that validate your solution after you finish. You can program in essentially whatever language you feel most comfortable in (C#, Java, VB, C++), and a practice room is available if you need some time to get used to things. “Real” competitions are scheduled regularly.

The hardest of these three exercises I just completed was an English to “Taglish” translator. It essentially just does some verb conjugation and other hackery to transform an input string. My solution can be seen here. I encourage you to give it a try before looking. It's in the SRM 220 DIV 2 set of problems.

What's amazing is how elegant and ugly solutions to the same problem can be. (The code I have shared is certainly in the latter category! ;) ) Once you submit your answer, you can take a look at what other folks submitted.