As a part of my summer project, I've had to search for website that will level my classroom library books. Our school system uses the Fountas and Pinnell Guided Reading levels, so I tried to find a few sites that would level as many books as possible. Being the frugal teacher type, I was looking for free sites. This is what I found:
Beaverton Leveled Book Database - The Beaverton School District has a fantastic site that allows you to search by title, author, or publisher, as well as guided reading, DRA, or Lexile level. Searching by each of the six traits is also an option.
A to Z Teacher Stuff Leveled Book Database - Another great leveling site where you can search by title, author, keyword, guided reading level, or reading recovery level.
Scholastic Book Wizard - Enter a title, author, or keyword and you can find the guided reading level, DRA, lexile measure, or grade level equivalent. You can also search for similar books or books by reading level.
Fountas and Pinnell Leveled Books - $25/year to subscribe to this website, so I can't tell you exactly what it's like, but it IS the official F&P book leveling site.