Something I've found during the annual catalogue inundation that I thought might appeal to gifted kids (and adults):
Edmund Scientifics, where you can always find a winner, is offering a K'Nex Value Tub. 275 pieces for $19.99. This is a temporary overstock sale, so get them before they're gone.
For little bug-lovers: Exobonz is an award-winning building set made up of bug parts, rather than the usual blocks or sticks (like K'Nex). I just found this in the National Geographic gift catalog.
They also offer a pair of remote-control Tarantulas whose eight hairy legs move independently, just like the real thing. ICK! (Btw, I've seen single RC tarantulas in other kids' catalogs, too, for less than half what the $48 Nat. Geo wants. Check Google.)
Future engineers might be interested in the Chaos Tower, a giant Rube Goldberg-like device you design yourself. Think the Mousetrap game, but motorized. The best price I've seen for this is from American Science and Surplus, where they call it the Rube Goldberg Kit. Or Google "Chaos Tower."
Another fun one from AS&S, where we're getting most of our gifts this year, is the model trebuchet. Clearly anything that flings things through the air is worth having. Since Wolfie and Xavier have both come across siege weapons in their social studies course, they're very excited about this.
Finally, the must-have gift for ever-so-hard-to-buy-for 12 year old boys this winter is the pocketed security sock, again from National Geographic. Go figure, but my boys were all oohs and aahs about socks with zippered pockets in them. And at 3 pair for $30, they're a perfect...stocking stuffer?