Bulfinch's Mythology was one of my favorite books growing up. It and Grimm's Fairy Tales :)
He does a neat retelling of the Arthurian and the Roland stories as well as the greek myths. His idea was to create a source where people who may not have had a chance to read all these legendary works what all the hubbub was about. Very useful reference when we might not even heard of some of this stuff...like the stories about Roland have just about died into obscurity, although the King Arthur stuff still lives - but they are worth knowing!