Paul Collins (of Weekend Stubble blog-fame) offers up quite a fantastic cast of forgotten characters in his 2001 book Banvard's Folly: Thirteen Tales of Renowned Obscurity, Famous Anonymity, and Rotten Luck. Collins writes in the preface that he grew curious about all the "other" people that one finds mentioned in historical documents - not the ones we know, but those we've never heard of: "... buried in these footnotes of history are brilliant, fatally flawed thinkers who rose to dizzying heights of intellect and even fame, only to come crashing down into disaster, ridicule, or just the utter silence of oblivion."
From George Psalmanazar, an eighteenth-century Dutch huckster who pretended to be from Formosa and fooled most of London for a few years (and even wrote a lengthy history of the island made up of complete nonsense) to Concord grape developer Ephriam Wales Bull and Civil War veteran A.J. Pleasonton - who was convinced that sitting under blue glass would cure what ails you - and beyond, Collins' subjects never fail to amuse, intrigue, and tickle the curiosity. As a source of short character sketches of these folks, it seems unlikely that Banvard's Folly will be surpassed anytime soon.
While there were a couple of minor errors in the book (Edgar Allan Poe's death was not caused by rabies - even if that theory has come into popularity recently - and Jefferson was not inaugurated in 1806), Collins has done his research well, and it shows. I don't hesitate at all in recommending this book; it's well worth a read.