This is so subtle you need to bring your magnifier!
Source Carlos Valdez
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
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
This is the remix of "polka dot seamless pattern".The image depicts polka dot seamless pattern.
Source Yamachem
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Here's a dark background pattern that contains a steel grid pattern as a texture. Use it as a website background or for other purposes. It's free!
Source V. Hartikainen
Prismatic Polyskelion Pattern No Background
Source GDJ
This white background pattern has a seamless grunge style texture. Here's a white grunge style background pattern. Use it as a tiled background image on web sites or for other purposes.
Source V. Hartikainen
Remixed from a drawing in 'A Girl in Ten Thousand', Elizabeth Meade, 1896.
Source Firkin
Super dark, crisp and detailed. And a Kill Bill reference.
Source Badhon Ebrahim
Inspired by a pattern found in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
This background pattern has futuristic look. So, maybe it could be used on websites or blogs dedicated to video games?!
Source V. Hartikainen
Here is a new seamless wood texture for using as blog or website backgrounds.
Source V. Hartikainen
Remixed from a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
Luxury pattern, looking like it came right out of Paris.
Source Daniel Beaton