Courtesy of the Library of Congress, 2,100 early baseball cards dating from 1887 to 1914.
And here's a nifty site that includes some 30,000 vintage baseball card photos (click the "OBC Specials" button), and an article about Topps, the all-time king of baseball cards, and some of their more obscure card sets and collections (click their "Library" button, then select the "Topps Insert, Test And Supplemental Baseball Issues 1949-1980"). It sounds dry, but there's a ton of interesting history to be found inside.
Years ago (1938 to be precise) four brothers, Abram, Ira, Joseph and Philip Shorin, erstwhile cigar manufacturers, established a chewing gum company in Brooklyn (where else?). Wanting to select a name that would let the public know how good their gum was and they settled on Topps (the extra "p" was for effect) and unwittingly created what was to become the largest bubble gum card entity in the Western Hemisphere. At some point, most probably toward the end of World War II, or just after, they began marketing their famous Bazooka bubble gum and yet another American institution was born. Looking for ways to increase product exposure, Abram hit upon the idea of packaging their bubble gum with trading cards. This was in 1948 and things have never been the same...