The inquisitive people in your life are surprisingly easy to buy for if you can tap into what motivates them. And what motivates them is, simply, curiosity. Buy them something that occupies their mind or intrigues them and you've got it right. I've got some suggestions that fit the bill.
1. Things Come Apart: a Teardown Manual for Modern Living, Hardcover
By Thames Hudson $23 on Amazon
For that person in your life who loves to tinker with a screwdriver. Beautiful photos of the intricate innards of 100s of things.