A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
A very dark asfalt pattern based off of a photo taken with my iPhone.
Source Atle Mo
A grayscale fabric pattern with vertical lines of stitch holes.
Source V. Hartikainen
An abstract pale yellow paper-like background with stains colored in yellow and green.
Source V. Hartikainen
From a drawing in 'Cowdray: the history of a great English House', Julia Roundell, 1884.
Source Firkin
Luxurious looking pattern (for a T-shirt maybe?) with a hint of green.
Source Simon Meek
A dark pattern made out of 3×3 circles and a 1px shadow. This works well as a carbon texture or background.
Source Atle Mo
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
You could get a bit dizzy from this one, but it might come in handy.
Source Dertig Media
Looks like an old rug or a computer chip.
Source Patutin Sergey
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Prismatic Abstract Geometric Background 4
Source GDJ
Prismatic Snowflakes Pattern 3 No Background
Source GDJ
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
I took the liberty of using Dmitry’s pattern and made a version without perforation.
Source Atle Mo
More in the paper realm, this time with fibers.
Source Jorge Fuentes
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
Number five from the same submitter, makes my job easy.
Source Dima Shiper