Randall Munroe makes science fun. This is a must-read for anyone who considers themselves a geek. The only question is what format. My wife and I got both the hardback, for the images, and the audiobook so that we could listen together. Bonus, the audiobook is narrated by… Drum roll, please… Wil Wheaton. You know, Shutup Wesly from Star Trek:TNG. Wil provides great enthusiasm in his narration.
In case you haven’t already read the original What If?
Randall also has the book How To that is filled with lots of science and engineering fun. You can get all three of his hardcover books from Amazon for $48. They would make a fantastic gift for any geek friend/relative.