This has the makings of a great thread. Some terrific photos so far. Here's my faves . . .
#1: 1930 Old Timers Game at Boston.
Similar to Matt's. Just won it the other week. There is a ton of baseball history in this photo; you can stare at it for hours.
#2: Team photo of the 1928 San Francisco Seals printed from original glass negative. Some talented ballplayers in this crew.
#3: Harry M. Stevens outfield panorama of Yankee Stadium in 1939. It didn't look much different, except for the scoreboard, when I was a kid twenty years later, and is still one of the most beautiful vistas ever beheld by these eyeballs.
Honorable Mention:
Babe and Kids, 1923
Prince Oana warming up his flamethrower, Aratani team in Japan, 1920's