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
Remixed from a drawing in 'Jezebel's Daughter', Wilkie Collins 1880
Source Firkin
A seamless texture of a rough concrete surface.
Source V. Hartikainen
A black tile-able background with paper-like texture.
Source V. Hartikainen
You know I love paper patterns. Here is one from Stephen. Say thank you!
Source Stephen Gilbert
Dark pattern with some nice diagonal stitched lines crossing over.
Source Ashton
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
Number five from the same submitter, makes my job easy.
Source Dima Shiper
Here's a tile-able wood background image for use in web design.
Source V. Hartikainen
Prismatic Abstract Geometric Background derived from an image on Pixabay.
Source GDJ
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
Formed from decorative divider 184 in paint.net. Vectorised with Vector Magic.
Source Firkin
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
Prismatic Polyskelion Pattern No Background
Source GDJ
A smooth mid-tone gray, or low contrast if you will, linen pattern.
Source Jordan Pittman
One can never have too few rice paper patterns, so here is one more.
Source Atle Mo
Prismatic Hexagonalism Pattern No Background
Source GDJ