Energy Lab for Kids by Emily Howbaker
I've evaluated a lot of kids' science experiment books and this is one of the better ones. It succeeds on a number of fronts.
1) It has a clear theme. From the title onward, you know exxactly what sort of experiments you are getting.
2) The steps for each experiment are clearly explained and supported by photos.
3) Each experiment is accompanied by the scientific explanation for what participants will observe.
I could see using this book to supplement homeschooling curriculum or as a part of a summer education program, not to mention just being fun for science minded kids.