Pretty broad question 
I'd enjoy anything that has a definite shape (i.e., is an enclosure, in some kind of box), has some types of buttons, and has a classic feel to it.
It's almost impossible to go wrong here. You can get 10 things, let him pick 1 or 2 that he likes, and re-sell the rest
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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons