The Book Adventure site is a free, reading incentive program dedicated to encouraging kids in grades K-8 to read.  Created by the Sylvan Learning Foundation and sponsored by well known educational associations and corporations,  it is designed as a resource for both teachers and parents to help kids succeed in reading.

Kids have over 5,400 titles and descriptions of popular books to choose from.   They then read the books offline.  Once they've finished the book, they can return to the site and take a multiple choice quiz on each book they read for prize incentives.                  
                 
The Teachers Lounge is a great resource for creating reading lists for students.  The Book Finder tool allows the searching of over 5,400 books by grade level, (K-8), reading level, fiction or non-fiction, genre (37 categories ranging from Action & Adventure Art & Architecture Boys & Men Ethnic Studies Girls & Women to Mysteries & Detective Stories Social Situations & Growing Up Sports & Recreation and more), title and ISBN.