Seven Books Lost to History

From Cracked: 7 Books We Lost to History That Would Have Changed the World. I have more trust in Cracked's skill at humour than I do at research, but it's still a good read. I like Ab urbe condita libri and the rare books section of the Grand Library of Baghdad, which was 'the Library of Congress of its time' according to this article.

This page is not entirely safe for reading at work (NSFW).