As the resident programming challenge junkie, I feel the need to point out all the cool contests when they come up.
The Internet Problem Solving Contest just started accepting registrations today for their event on March 13th. I've entered this event in the past and consider it to be a fun little brain bender.
The contest generally involves around eight problems most of which will have easy and hard variations. The format is that they describe the problem and provide the input. All they want back is the output, so you can use any tools you like.
You can look over the old problems in the "ARCHIVE" link at the top of their site. Here's a link:
Hope to see a few Rubists competing!
James Edward Gray II