A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
Zero CC tileable ground (#2) cracked, crackled texture, made by me. CC0
Source Sojan Janso
A new take on the black linen pattern. Softer this time.
Source Atle Mo
Just what the name says, paper fibers. Always good to have.
Source Heliodor jalba
Sharp diamond pattern. A small 24x18px tile.
Source Tom Neal
Prismatic Polyskelion Pattern No Background
Source GDJ
Prismatic Chevrons Pattern 5 With Background
Source GDJ
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
Number 4 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
This was submitted in a beige color, hence the name. Now it’s a gray paper pattern.
Source Konstantin Ivanov
Number 5 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Remixed from a JPG that was uploaded to Pixabay by susanlu4esm
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin