Online Programming Contests

Creative Commons stopwatch by Gaetan Lee(in no particular order)
[*][url=]Sphere Online Judge[/url]
Supports more than 30 different programming languages and a growing problem-set of about 3000 tasks for practice.
[*][url=]Project Euler[/url].
A “series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve”.
[*][url=]UVa Online Judge[/url]
More than 200 contests and more than 2000 algorithmic programming problems.
Not only algorithmical, but also architectural and design contests.
Happy coding!

If you still haven’t got enough, check out the [url=]Google Directory of Programming Contests[/url].