It's funny, the best gift I can think of seems really stupid. When I was in second or third grade, I had an uncle who was an accountant, and he gave me a paperback book of mathematical tables (trig, logs, etc), with instructions on how to interpolate values and an introduction to algebra and analysis. It was way beyond anything I'd had in school yet. I loved that book, read the text parts over and over until it was literally falling apart. I can't even imagine what a little nerd I must have been for that to seem like a reasonable gift, but that book and I were inseparable