I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
A seamless texture of an abstract wall colored in shades of light orange brown.
Source V. Hartikainen
Zero CC tileable grass texture, photographed and made by me. CC0
Source Sojan Janso
Stefan is hard at work, this time with a funky pattern of squares.
Source Stefan Aleksić
Remixed from a drawing in 'Analecta Eboracensia', Thomas Widdrington, 1897.
Source Firkin
Remixed from a drawing in 'Analecta Eboracensia', Thomas Widdrington, 1897.
Source Firkin
A free grid paper background pattern for using on web sites.
Source V. Hartikainen
We have some linen patterns here, but none that are stressed. Until now.
Source Jordan Pittman
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Derived from a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Non-seamless pattern drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Remixed from a drawing in 'Some account of the Worshipful Company of Ironmongers', John Nicholl, 1866.
Source Firkin
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Sometimes you just need the simplest thing.
Source Fabricio
A seamless pattern formed from miutopia mug remixes on a tablecloth.
Source Firkin
Bright Multicolored Floral Background by Karen Arnold from PDP.
Source GDJ