This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby
Sort of reminds me of those old house wallpapers.
Source Tish
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
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
A free grid paper background pattern for using on web sites.
Source V. Hartikainen
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ
From a drawing in 'Uit de geschiedenis der Heilige Stede te Amsterdam', Yohannes Sterck, 1898.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
By popular request, an outline version of the pentagon pattern.
Source Atle Mo
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
Some rectangles, a bit of dust and grunge, plus a hint of concrete.
Source Atle Mo
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Zero CC tileable wood texture, made by me procedurally in Neo Texture Edit.
Source Sojan Janso
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
Derived from a JPG that was uploaded to Pixabay by ractapopulous
Source Firkin
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
Formed by heavily distorting part of a an image of a fish uploaded to Pixabay by GLady
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The original enhanced with one of Inkscapes's filters.
Source Firkin