Tontie deserves its own entry—and this way I can also add it to the "Recommended" section in the side bar. Posted a while back with the magnificient Grow game by Eyezmaze, Tontie is simply one of the most accessible, fun-to-play and challenging Flash games I've seen. Anyone with a numeric keypad can play: Just follow the on-screen instructions for each level by pressing the corresponding keys when directed. Each level adds more complexity and variety, so be alert as you play. Wonderful. Simple. Cute.
Update: A new version of Tontie has been released.