One of our new favorite apps is EasyBib. If only it had been around when we were in grad school! EasyBib allows users to "create accurate MLA, APA, and Chicago style citations in seconds by scanning a book bar code or by typing the name of a book." Once you've scanned your book, you can either email it to yourself or upload it to EasyBib's bibliography management site.
EasyBib works with iPhone, iPod Touch and iPad, though their notes say it works best with iPhone 4. EasyBib is available free in the AppStore.