Here's a dark background pattern that contains a steel grid pattern as a texture. Use it as a website background or for other purposes. It's free!
Source V. Hartikainen
From a drawing in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
Sweet and subtle white plaster with hints of noise and grunge.
Source Phil Maurer
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Remixed from a raster on Pixabay that was uploaded by ArtsyBee.
Source Firkin
A seamless web texture of "green stone".
Source V. Hartikainen
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
Lovely pattern with splattered vintage speckles.
Source David Pomfret
Bigger is better, right? So here you have some large carbon fiber.
Source Factorio.us Collective
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Can never have too many knitting patterns, especially as nice as this.
Source Victoria Spahn
A version without colours blended together to give a different look.
Source Firkin
This background has abstract texture with some similarities to wood.
Source V. Hartikainen
This background pattern contains a seamless texture of bark. It's not very realistic, but I think it looks quite nice.
Source V. Hartikainen
A nice and simple gray stucco material. Great on its own, or as a base for a new pattern.
Source Bartosz Kaszubowski