bookwizard from Scholastic
You can punch in a book that your kids have really enjoyed and the level you want them to be reading next. For example, my kids have loved Magic Tree House. But 2 of my kids can now read them in one bathroom sitting. I can use this bookwizard to type in "Magic Tree House" but then I type in what level I want the search to include. For us, I will type in 3 grade levels above Magic Tree House.
Voila! The bookwizard lists out the books of similar story lines, but more age appropriate for my kids. It's like having a personal librarian without the hair bun, glasses on a chain and the snide comments about the Michael Jackson Fan book that you wanted to check out every week of second grade.
Some of us still have scars.