One of the favorite Christmas gifts the 2 y/o received has been her Aquadoodle Draw 'N Doodle Mat. It's a pretty simple concept really. The felt tipped pen is filled with water, and then is used to draw 'n doodle on the mat. The mat is nothing more than thin white fabric stretched over a bright blue plastic background. The water causes the fabric to cling to the background and shows the bright blue through. The toy only uses a small enough amount of water that the 2 y/o couldn't possibly make a big mess with it, and the whole thing can be used over and over as the mat dries out.
Pretty ingenious. Maybe it's only because I'm a big dumb male, but I have to wonder if the whole concept wasn't conceived in the middle of a wet T-shirt contest!!