One resource that might be very helpful for you is a book called Leveled Books for Readers Grades 3-6, by Fountas and Pinnell (Heinemann, 2002). It lists over 6,000 books and gives the author, reading level, publisher, and genre of each. The genres that are included are: "traditional literature," "realistic fiction," "historical fiction," "science fiction," "fantasy," "biography," and "information book." The nonfiction listings in particular might be a good fit for your students. You may find that many of the books listed are available in your school's library or in your local public library.

Also, check out the publishers of what are called "high interest/low readability" texts. These are books that are written on a first to third grade reading level but treat themes and topics that are of interest to students of middle school or high school age. An internet search will yield a variety of publishers that specialize in this type of text.