If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Derived from an image that was uploaded to Pixabay by darkmoon1968
Source Firkin
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
This seamless pattern consists of a blue grid on a yellow background.
Source V. Hartikainen
This is the remix of "Colorful Floral Pattern Background 3" uploaded by "GDJ". Thanks.
Source Yamachem
Zero CC tileable grass texture, photographed and made by me. CC0
Source Sojan Janso
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
Drawn in Paint.net and vectorised in Vector Magic
Source Firkin
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
Prismatic Groovy Concentric Background 3
Source GDJ
The perfect pattern for all your blogs about type, or type-related matters.
Source Atle Mo
Zero CC tileable hard cover red book, scanned and made by me. CC0
Source Sojan Janso
Remixed from a drawing that was uploaded to Pixabay by ractapopulous
Source Firkin
Prismatic Abstract Background Design
Source GDJ
As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
A bit simplified version. Although it could be edited out to be simpler. Anyway, this time the tiling is converted to a pattern fill -which is using clipping for the tile's edges.
Source Lazur URH
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
A light gray fabric pattern with faded vertical stripes.
Source V. Hartikainen
More bright luxury. This is a bit larger than fancy deboss, and with a bit more noise.
Source Viszt Péter