Leaf produced a handsome trading card set devoted to Star Trek in 1967, while the series was still on the air. Unfortunately, they printed the cards before they had secured the license to do so - and, as it turned out, they didn't get the final permissions. So, although many cards have made it into collectors' hands, the set is considered very difficult to complete, and individual cards are expensive.
The card fronts featured a still photo taken from the show, in black and white, with teh card title in a black band at the bottom and a wide white border along the card edges.
The backs were white, with the card title and a paragraph of text about the photo in the center, with the Starfleet emblem at the upper left and a smaller photo of Kirk and Spock on the right. All card backs were horizontal.
Note that prices on this card set are speculative, given their scarcity and the waxing and waning of interest over time for whatever reason.