Inference Riddle Game is a site created by Phil Tulga that has 15 inference riddles.  The user can decide which riddle to work on by typing in a number, and can slowly add clues until he or she guesses the answer, types it in, and checks it.  This would be fun to play with the class when there is a small wait time for something.  When I play games like this with my students, I always ask them to justify their guesses.  They are also discouraged from “wild guesses” by being told they will be out of the game if they guess incorrectly.  Another way to use this site would be as a springboard for students to create their own riddles – perhaps using Powerpoint or another presentation option – that are related to something that is being studied.