BK-

Around that age, my boys started enjoying Larry Gonick's Cartoon Histories and Guides. We have all of his history books (and they do contain some controversial bits, such as descriptions of Spartan warriors having sexual relations with young boys, so you may wish to preread or avoid for a few more years) and the cartoon guide to physics and chemistry. My daughter doesn't care for these books, but my boys eat them up.

I reviewed a periodic table book for kids recently. See here:
http://www.bellaonline.com/articles/art52723.asp

Old college textbooks can be fun to peruse too. If you don't have any, you can try asking for them on freecycle or at the local college. When required books are replaced with newer texts, the older books may just get tossed.

hth-

Lorel