This site was the first hacking challenge for me. I completed all challenges years ago but I did had help from Google and books from the library. I remember that for each challenge I had to do research and a lot of reading in order to pass to the next level.
http://www.hackergames.net/ is a big list of similar sites my favourite was http://www.hackthissite.org some fun challenges there most but not all hacking related, nice "real world" senarios, and logic puzzles. Lost a lot of sleep with that one. If memory serves there were about 50~60 challenges.
As with most of these sites you'll get a mix of idiot script kiddes and very helpful people using them. (not all whitehats, you have been warned)