Can you provide any further information about what the app is for? When I saw your question earlier I did a search of "AppShopper," Edited by Moderator ~ no external links, please.
Lots of hits to manage the books you've checked out from your local library and apps for specific libraries (mainly universities) to determine if particular books are in their collections. But I don't think that's what you have in mind.
If you're hoping to download "free" books, you might try one of the e-Readers. Kobo is especially good for these. In general, if you're looking for "classics," published before 1923 you can almost always find free copies available on the net. Just put the Kobo app on your iPad. You can also access the Kindle library with lots of free books if you use Safari to go to the kindle site and save the bookmark on your iPad screen.
In addition "Project Gutenberg" has about 36,000 books that can be downloaded free of charge and read with one of the e-Readers available for the iPad. They have a great search capability for their books.
MobileReader Devices How-To - Gutenberg
Looking for more focused research resources? Although you can certainly do that sort of search on your iPad, you may find it easier to work with a computer and examine some of the tools Google has developed in their labs. (I find the browser limitations on the iPad to be constraining.) Once you've found something interesting, just take a note or send yourself an email that you can then access from your iPad.
