WordNet (r) 3.0 (2006):

letterhead
    n 1: a sheet of stationery with name and address of the
         organization printed at the top

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "letterhead":
   address, billhead, book stamp, bookplate, brand, broad arrow,
   cachet, check, colophon, counterfoil, countermark, destination,
   direction, docket, government mark, government stamp, hallmark,
   imprint, label, logo, logotype, masthead, name and address, plate,
   postal zone, price tag, registered trademark, running head,
   running title, seal, sigil, signet, stamp, sticker, stub,
   superscription, tag, tally, ticket, title page, token, trade name,
   trademark, trademark name, zip code, zone