Here's something fun - my favorite puzzle in the world (little known fact about me - I won the Fifteen Puzzle contest for my entire school when I was twelve years old! It was actually quite funny, there were training sessions conducted by the teachers for those [boys!] who were trying to beat me, but no one could do it) - anyway - this version is done in Silverlight, with an explanation article on how the code was written as well. Although this version is slick, I must say that I prefer the original, metal one.
In fact, I often carry one of these in my bag.