Call me a big nerd, but I like game related stuff, like I just ordered myself a Warthog toy from Halo3, but I have a few bits and bobs, a ghost with a Brute sitting in it, Leon from RE4 etc etc. I'm not a collector, I just like to have the stuff from my favorite games.
Personally I'd just go on Amazon or something and find a figure from one of his favorite games - it's much less embarrassing when people buy you them as gifts, they make great desk space wasters
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Something else PC related you might want to look into is these desktop missile launchers, you get a little missile launcher that plugs in to USB, then you control it from your PC, bzzzzzt, bzzzzt, aim, FIRE! - household pets beware!.