Robot Turtles is great (and now available at Target). But, I think it is really best for kids between ages 3-5. My six year old can breeze through it and gets bored quickly, even with the harder rules. However, my 4 year old loves telling us how to move her turtle.
For older kids that find Robot Turtles too simple you could try Robot Rally. You can really tell the difference when you're playing with a mix of programmers and non-programmers.