I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
A dark brown fabric-like background texture with seamless pattern of winding stripes.
Source V. Hartikainen
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A light background pattern with diagonal stripes. Here's a simple light striped background for you.
Source V. Hartikainen
A free seamless background image with a texture of dark red "canvas". It should look very nice on web sites.
Source V. Hartikainen
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Prismatic Abstract Geometric Background 2
Source GDJ
Remixed from a drawing in 'Works. Popular edition', John Ruskin, 1886.
Source Firkin
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
Semi-light fabric pattern made out of random pixels in shades of gray.
Source Atle Mo
Number 3 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
It was called Navy Blue, but I made it dark. You know, the way I like it.
Source Ethan Hamilton
The tile this is formed from can be retrieved in Inkscape by selecting the rectangle and using shift+alt+i
Source Firkin
An abstract web texture of a polished blue stone (or does it look more like ice).
Source V. Hartikainen
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Classic 45-degree pattern, light version.
Source Luke McDonald
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
Sometimes you just need the simplest thing.
Source Fabricio
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo