http://www.cm.cf.ac.uk/htbin/AndrewW/Puzzle/puzzle4x4image
This site offers a 4x4 tile puzzle which the user can complete by clicking on individual tiles with the goal of fixing a scrambled image. The page, including all of its images, reloads every time one clicks on a tile, so this site requires above-average bandwidth. The site also links to some information about the puzzle and how it works, and to a collection of more sliding tile puzzles.