National History Education Clearinghouse - Site created by George Mason University with Best Practices, Teaching Materials, Research, Professional Development
While the main purpose of the site are some technology sites that will help with writing, take a look at the Sidebar Sites. They are really worth looking at. By the way, if you're not subscribed to edudemic, think about doing so.
To get a better selection of books, it's best to add a Lexile measure as well as the Range. You can get a Range by using Current Grade and then clicking on one of the three buttons: difficult, just right, easy. Then pick a number within the range, lower to higher, depending on the student, group, or class