I'd like to recommend the Secret Science Alliance by Eleanor Davis. It's about 3 kid inventors (one uber geek, one super cool genius girl, and one 2e jock) who have to protect their inventions from a rival scientist. It's comic book style so it's dense with images, but I think it's over 100 pages long. I think it's the sort of book that kids (especially gifted kids) can get a lot out of. Inspired by the book, we started building ("inventing") robots!