This app, available for iPhone, iPad, and Android promises to help you keep track of checking out books, leveling books, and finding the right books for your students. For more information on this $0.99 app before purchasing, read here and here.
http://www.chiisai.com/ This app won't level books for you, but it will help you keep track of your library--at school or home. There are also options for listing books you want to buy and books you want to read as well as recommendations. I am trying it to keep track of my coaching books--which belong to which school or the district. Scanning barcodes is an easy way to input the books!
http://www.scholastic.com/teachers/ Click on "book wizard" on the left of the page. Then choose a leveling system (Lexile, Guided Reading, DRA), enter book and voila! you get a level. There is also a feature for matching similar books. Scholastic is working on a phone/iPad app version of this wizard also. Looking forward to that!
Did you know there is a tab called Books in this teacher tool? This is the resource you use to look up SRI/SRC information on your students, but if you use the Books tab, you can also look up just about any book Scholastic ever published to find Lexile and other leveling information.
http://titlewave.com/login/ This database is part of the Follett Library Resources. You will have to create your own free account, but then you will have access to this highly comprehensive database of books. This resource gives Lexile, and other leveling information. You can search by title, author, reading level, etc