A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
Nice little grid. Would work great as a base on top of some other patterns.
Source Arno Gregorian
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a drawing in 'Analecta Eboracensia', Thomas Widdrington, 1897.
Source Firkin
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
A repeating background with dark brown stone-like texture and abstract pattern that looks like tree trunks.
Source V. Hartikainen
A simple but elegant classic. Every collection needs one of these.
Source Christopher Burton
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
Crossing lines with a subtle emboss effect on a dark background.
Source Stefan Aleksić
I asked Gjermund if he could make a pattern for us – result!
Source Gjermund Gustavsen
Derived from a JPG that was uploaded to Pixabay by ractapopulous
Source Firkin