From a drawing in 'A Guide to the Guildhall of the City of London', John Baddeley, 1898.
Source Firkin
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A heavy dark gray base, some subtle noise and a 45-degree grid makes this look like a pattern with a tactile feel to it.
Source Atle Mo
Prismatic Hypnotic Pattern 2 No Background
Source GDJ
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Nothing like a clean set of bed sheets, huh?
Source Badhon Ebrahim
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
A very slick dark rubber grip pattern, sort of like the grip on a camera.
Source Sinisha
Zero CC tileable hard cover cells, skin like, book texture. 4K, Scanned and made by me CC0
Source Sojan Janso
Zero CC tileable ground (#2) cracked, crackled texture, made by me. CC0
Source Sojan Janso
Luxurious looking pattern (for a T-shirt maybe?) with a hint of green.
Source Simon Meek
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A free web background image with a seamless concrete-like texture and an Indian-red color.
Source V. Hartikainen
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
One can never have too few rice paper patterns, so here is one more.
Source Atle Mo
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
From a drawing in 'Codogno e il suo territorio nella cronaca e nella storia'', Gio and Giarella Cairo, 1897.
Source Firkin
An alternative colour scheme to the original seamless pattern.
Source Firkin
Abstract Ellipses Background Grayscale
Source GDJ