Probably my top/fav postcards...
1907 Seamless Steel Tubes Cobb (mailed by Cobb himself)
1915 Red Sox postcard (Ruth as a rookie)
1903 NY Giants at the Waldorf Astoria (first known mlb team to appear on a postcard)
1911 Addie Joss Day Postcard (includes Joe Jackson and Cobb in a Cleveland uniform)
1908-11 Bregstone Rube Waddell (my favorite pre-war player)