It's not a book, but my 10- and 13-year-olds LOVE PBS's Rough Science series, which presents a group of scientists with a new set of challenges each week (e.g, gold panning, making metal detectors, etc). Some of the episodes are on Netflix and can be checked out from the Seattle library (both DVD & digital media). Here are a couple companion websites: http://www.pbs.org/weta/roughscience/series/
http://www.open2.net/roughscience/
My kids also enjoy magazines like Ask (for somewhat younger kids), Odyssey, and Ranger Rick. I think the thrill of getting something in the mail, combined with the graphics and smaller volume size of magazines makes these appealing.