Same classic 45-degree pattern, dark version.
Source Luke McDonald
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
This reminds me of Game Cube. A nice light 3D cube pattern.
Source Sander Ottens
Sort of reminds me of those old house wallpapers.
Source Tish
Prismatic Polka Dots Mark II 3 No Background
Source GDJ
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A free seamless background texture of "timber wall" (colored in dark brown).
Source V. Hartikainen
A re-make of the Gradient Squares pattern.
Source Dimitar Karaytchev
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
Orange-red pattern for tiled backgrounds.
Source V. Hartikainen
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Prismatic Polka Dots Mark II No Background
Source GDJ
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
A seamless pattern with a unit cell drawn as a bitmap in Paint.net and vectorized in Vector Magic.
Source Firkin
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
Another fairly simple design drawn in Paint.net and vectorized in Inkscape.
Source Firkin
Remixed from a drawing in 'Works. Popular edition', John Ruskin, 1886.
Source Firkin
Prismatic Groovy Concentric Background 5
Source GDJ
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
Sounds like something from World of Warcraft. Has to be good.
Source Tony Kinard
Embossed lines and squares with subtle highlights.
Source Alex Parker
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler