Steven Heller calls himself a "letterhead" — that is, someone who collects letterhead (compare with "Deadhead"); his brief reflections on his passion for Design Observer and interesting and well-observed, but they're not a patch on the actual samples of beautiful, bygone letterhead from his collection.
Letterhead collectors are not a monolithic cult. Each has his or her special needs. Some collect only corporations and institutions, other subsets are just design firms, and others are just design firms that start with the letter P. Collecting can get obsessively granular. There are collections of 19th century, political party and automotive letterheads, among others. You name it and someone collects it. There are many books on the art and design of letterheads. My favorite is Leslie Carbaga's 1992 Letterheads: One Hundred Years of Great Design, 1850-1950. I also cherish The Avant Garde Letterhead by Elaine Lustig Cohen and Ellen Lupton (catalog of the 1996 Cooper Hewitt exhibition of Lustig's modernist letterhead collection now in the MoMA permanent collection). Then there are dozens of richly stocked paper company sample books that contain printed examples on numerous paper weights, colors and textures. Usually these specimens are blank — many collectors prefer blank pages. But others prefer writing and signatures too. This is where the rarified field of autograph collection intersects with "letterheading."
Confessions of a Letterhead [Steven Heller/Design Observer]