I found the best book last Christmas. My DS reads it over and over. It is Cool Stuff and How It Works, by Chris Woodford, James Flint, Ben Morgan, Clint Witchalls, and Luke Collins. I got it at Barnes and Noble.com for $24.99 (hardcover). It tells how mp3 players work, microwaves, TVs, planes, hurricanes, etc... It has great pictures of the inside of things. Also, nobody has mentioned my favorite website that I learned about here: bookcloseouts.com. I love this site. If you know what you are looking for its great. I have found many wonderful books for $1.99 or $2.99 each. Becareful not to be tricked into junk books! I always look up the books at Barnes and Noble.com and/or Amazon.com for reviews. Good luck!