While going to the Comic Shop to start collecting "Skaar, son of Hulk", I stumbled upon Marvel: 1602, and loved it! I'm a big fan of both Neil Gaiman and colonial history, and this was fantastic(k) !
Somehow, that series led me to start collecting DC's Elseworlds...
Civil War: Atticus Kent as Superman in "Nation Divided" was intriguing, but "Batman: the Blue, the Grey, and the Bat" was by far my favorite Civil War story. Needed more characters from the Batman canon, but Wild Bill and Mark Twain hanging out with Mark Twain was good stuff!
Superman: Kal -- Superman landing in pre-Camelot England, is really, really great -- this one should have been a series!
And Batman: Leatherwing (a pirate tale) is interesting as well...
Anyone else have any favorite alterate histories?