The Last Man on Earth is the first movie to be based on the Richard Matheson book I Am Legend, about a post-apocalyptic world filled with vampires, and one dude fighting to stay alive. In this case, said dude is played by Vincent Price. It's probably the best version, although The Omega Man, the Charlton Heston one, is maybe a bit more fun, simply because its painful attempts to be groovy and "with it, man," are laughable now.
(The Will Smith one doesn't warrant comment.)
Watch it at 11:15PM on MGM's HD movie channel.