infodoodads pointed out this interesting website, ISBNdb.com. It currently has ISBN and basic information for over 3 million books, which it has gotten via scanning library websites, according to their FAQ. Something else mentioned on their FAQ is "'Books on the Same Shelf' -- it allows to quickly look up similar books in the same way they would be placed in a real world library. Currently, two classification systems are supported -- Dewey Decimal Classification (trademark of OCLC) and Library of Congress Classification."
Basically, it's a potentially helpful website, which I look forward to exploring.