"The connection between us and our kids and us and our parents and the fragility of that. It's no coincidence that it's a bookcase that is the symbol for that sequence in the film, because there's no better symbol for the repository of information passed down from one generation to the next. ... Books are a time machine." —Jonathan Nolan (IGN)

note: roughly the first half of these are the ones most prominently visible or confirmed/mentioned by Christopher Nolan; the second ~half consists of books identified by fans by zooming in in HD.

sources: Nolan Fans Forums StackExchange WIRED