ProjectEuler

[Arsener]

For beginners in programming this is an awesome site to tune your skills .http://projecteuler.net/index.php
I have already solved many problems on that site .

[FireintheHouse]

I've come across this before, back when i was taking a programming course. Worth checking out if you're pretty new to programming like I was (and still am lol).

[herlig]

It's a great site to train your algorithm-creating skills.. The difficulty varies from beginner to Intermediate