Few years back when I was god damn kid a friend of my told me about the site hellboundhackers.org. This site is so much fun. Besides large article base, it has numerous security challenges in different areas, from basic web hacking, java script hacking, encryption, timed, real world and steganography are on the list.
Going through the challenges teaches you about different vulnerabilities that are out there. And how to fix them – application patching challenges.
So go now, learn and exploit them already!