http://www.bookadventure.com/

Book Adventure is a FREE reading motivation program for children in grades K-8. Children create their own book lists from over 6,000 recommended titles, take multiple choice quizzes on the books they've read offline, and earn points and prizes for their literary successes. Book Adventure was created by the Sylvan Learning Foundation and is a non-profit organization.

Thanks Sara, that looks really interesting. The kids love books here, so I bookmarked it and will look at it with them in the morning.