Major League Baseball - 100 Years of the World Series (Collector's Edition)
This 2DVD set is an incredible value -- it has over 5 1/2 hours of great footage for around 15 bucks.  Whoever put this documentary together did a tremendous job of coming up with basically all of the actual footage of key plays and moments in the history of the World Series that you could ask for (even all the way back to the beginning), and tracked down interview footage from the key participants. I rated the 2DVD Yankee history set as also being essential -- basically, this makes an excellent companion.  The World Series set might appeal to baseball fans in general a bit more, because even though it has tons of Yankee footage (obviously), there is of footage of most of the guys you'd want to see (Mays, Aaron, Bonds, Williams, Brooklyn Dodgers/NY Giants, etc.)  Very compelling viewing, whether you're a novice fan or someone who has seen decades worth of baseball - it brought back a ton of great memories and makes you realize how often there are really great, historic moments in virtually every Series.