I've found that well-run hacking contests give a person the to oppurtunity expand his horizons, learn new skills and stay sharp. Depending on the contest, one can invest a significant amount of time in developing tools, techniques and other strategies during the course of the contest. Unfortunately, the tools and knowledge are often lost or forgotten once your answer is submitted. So, in an effort to counter this trend, I've decided to make a concerted effort to post my work in an accessible format.
The Ethical Hacker
Network Skillz contests are especially enjoyable.
Here are my answers and resources for a few: