Bibliodyssey has curated a beautiful collection of letterheads from 19th century and early 20th century architectural and industrial firms, doing a lot of cleanup and posting the hi-rez images to Flickr. The originals are from Columbia University's Biggert Collection.
The images in this post all come from Columbia University's very large assortment of commercial stationery (featuring architectural illustrations): the Biggert Collection.
The vast majority of the images below have been cropped, cleaned and variously doctored for display purposes, with an intent towards highlighting the range of letterform/font and design layouts. The underlying documents are invoices (most), letters, postcards, shipping records and related business and advertising letterhead ephemera from the mid-1800s to the 1930s.