A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
A tile-able background for websites with paper-like texture and a grid pattern layered on top of it.
Source V. Hartikainen
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Basket Fibers, Basket Texture, Braid Background style CC0 texture.
Source 1A-Photoshop
The image depicts a Japanese Edo pattern called "kanoko or 鹿の子" meaning "fawn" which has a fur with small white spots.
Source Yamachem
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin