Because I love dark patterns, here is Brushed Alum in a dark coating.
Source Tim Ward
Zero CC tileable dry grass texture, photographed and made by me. CC0
Source Sojan Janso
The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees
A black tile-able background with paper-like texture.
Source V. Hartikainen
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Textured Red Brown Plastic, Free Background Pattern. Although there's already enough plastic in our lives, let's bring it to the web too.)
Source V. Hartikainen
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
Zero CC tileable ground cracked, crackled, texture, made by me.
Source Sojan Janso
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Crossing lines with a subtle emboss effect on a dark background.
Source Stefan Aleksić
Prismatic Curved Diamond Pattern 5 No Background
Source GDJ
A comeback for you: the popular Escheresque, now in black.
Source Patten
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Sometimes you just need the simplest thing.
Source Fabricio
No, not the band but the pattern. Simple squares in gray tones, of course.
Source Atle Mo
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
This one looks like a cork panel. Feel free to use it as a tiled background on your blog or website.
Source V. Hartikainen
This was formed by distorting an image of a background on Pixabay.
Source Firkin
This is a remix of "blue wave-seigaiha".I hope this subtle color version of Seigaiha would be suitable for background .
Source Yamachem
Derived from a drawing in 'The Murmur of the Shells', Samuel Cowen, 1879.
Source Firkin
If you’re sick of the fancy 3D, grunge and noisy patterns, take a look at this flat 2D brick wall.
Source Listvetra