Here's a subtle marble-like background for use on websites.
Source V. Hartikainen
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Seamless pattern formed from a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
The image depicts a seamless pattern of the design which includes a stylized lotus and a stylized crane.I referred to the original image in a book which is into public domain.
Source Yamachem
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
A pattern drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
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 Geometric Pattern Background 2 No Black
Source GDJ
These dots are already worn for you, so you don’t have to.
Source Matt McDaniel
Derived from a JPG that was uploaded to Pixabay by ractapopulous
Source Firkin
Some dark 45 degree angles creating a nice pattern. Huge.
Source Dark Sharp Edges
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Pattern produced in Paint.net using the Vibrato plug-in.
Source Firkin
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
First pattern tailor-made for Retina, with many more to come. All the old ones are upscaled, in case you want to re-download.
Source Atle Mo
Alternative colour scheme for the original floral pattern.
Source Firkin
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male