A comeback for you: the popular Escheresque, now in black.
Source Patten
This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
Seamless Olive Green Web Background Image
Source V. Hartikainen
A background pattern with a look of rough fabric.
Source V. Hartikainen
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
A set of paper filters. The base texture is generated the same way, only the compositing mode is varied.
Source Lazur URH
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Love the style on this one, very fresh. Diagonal diamond pattern. Get it?
Source INS
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
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 cute x, if you need that sort of thing.
Source Juan Scrocchi
You know you can’t get enough of these linen-fabric-y patterns.
Source James Basoo