The tile for this is based on a repeating unit close to a design on Pixabay. It can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Can never have too many knitting patterns, especially as nice as this.
Source Victoria Spahn
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
A seamless pattern with a unit cell drawn as a bitmap in Paint.net and vectorized in Vector Magic.
Source Firkin
A pale yellow background pattern with vertical stripes. The stripes are partially faded. I think this background image turned out pretty well, especially those faded stripes.
Source V. Hartikainen
Luxurious looking pattern (for a T-shirt maybe?) with a hint of green.
Source Simon Meek
Prismatic Snowflakes Pattern 3 No Background
Source GDJ
Geometric lines are always hot, and this pattern is no exception.
Source Listvetra
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
The image depicts a seamless pattern of a tortoise in tortoiseshell (hexagon).
Source Yamachem
Abstract Tiled Background Extended 6
Source GDJ
I scanned a paper coffee cup. You know, in case you need it.
Source Atle Mo
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
Almost like little fish shells, or dragon skin.
Source Graphiste
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
Prismatic Chevrons Pattern 5 With Background
Source GDJ
You may use it as is, or modify it as you like.
Source V. Hartikainen