From today a very new challenge site is participating in the global ranking: Rosecode.
It offers math and programming challenges only, and new interesting problems shall be added frequently, so it is similar to project euler.
Most problems require you to code a bit to compute the correct answers, but knowledge of math is most often required to come up with an efficent algorithm that can solve a problem within reasonable time.
Many thanks go out to elasolova for writing the needed scripts, and i wish all others: