Compact Chimney Climber (CCC)

You must have already thought about robots with wheels, tracks, 2-legged, 4-legged, fixed in place while sorting balls, LEGO bricks, drawing... But have you ever imagined a robot which doesn't touch the ground? So it's right here. CCC is built with a single NXT 2.0 set, from the instructions (building & programming) from The LEGO Mindstorms NXT 2.0 Discovery Book. It stops when it reaches the top (ultrasonic sensor) and it has a balance sensor, assembled with the color sensor. Here's it in action:

Baseball for 2

For those who love baseball and don't wanna to take the risk to splinter your house's windows, here is Baseball for 2. Built with only one NXT 2.0 set, it's controlled by two triggers idealized from this instructions (pdf), one for the thrower (armed with six Zamor spheres and a tire ro prevent balls flying through the air) and another one for the batter (with an auto-adjustable bat, with a color sensor that stops the motor when it "sees" the bat). A great model to play with your family and friends, with two spaces for the balls: the lower one, for the warded-off ones, and the upper, for the perfectly throwed ones. I recommend you to play on a towel, in order not to happen what you'll see in this video: