Jon - Blackguards and Red Stockings by William Ryczyk: This is another book that really opened my eyes to what was possible in the realm of baseball and non-fiction. It is a really good history of the National Association, the first professional baseball league. Pretty fascinating to see the troubles and chaos and compare it to the money-making machine that baseball is today.
Mark - The Last Nine Innings by Charles Euchner, Jr.: I thought that George Will's Men At Work took you inside baseball. Not like this one does. The things I learned. I can't recite them off the top of my head, but the author goes into detail about the forces behind pitching a ball. The strain on the body. He lays out with restrained minutia, but in terms that a layman can follow, statistics on the probability of a win, based on the events in the game (walk, hit by pitch, groundout, etc). He writes about the emergence of Latino players into the National Game. Reading it has made me watch baseball in a whole different light. Euchner does all this with the framework of game seven of the 2001 World Series, in which the Diamondbacks beat the Yankees. That setting is just the icing on the cake.
Jason - Baseball's Golden Age: The Photographs of Charles M. Conlon by Neal and Constance McCabe. Yes, it is a book of photos, but what glorious photos they are. The detail is so rich, you can see the pores on people's faces. For whimsy, you have Babe Ruth and Wally Pipp both posing with pieces of gum on the tops of their caps. But, the best pictures are the side by side looks at Charlie Gehringer nine years apart, with the same expression and you could swear that "The Mechanical Man" has not aged a day.