A comeback for you: the popular Escheresque, now in black.
Source Patten
The image is a remix of "edo pattern-samekomon".I changed the color of dots from black to white and added BG in light-brown.
Source Yamachem
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Here's a repeatable texture that resembles a light green concrete wall or something similar.
Source V. Hartikainen
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
To get the repeating unit, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Abstract Tiled Background Extended 8
Source GDJ
A dark brown fabric-like background texture with seamless pattern of winding stripes.
Source V. Hartikainen
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A bit of scratched up grayness. Always good.
Source Dmitry
Zero CC tileable bark texture, photographed and made by me. CC0
Source Sojan Janso
A very dark asfalt pattern based off of a photo taken with my iPhone.
Source Atle Mo
A free grid paper background pattern for using on web sites.
Source V. Hartikainen
The image depicts a seamless pattern of a snow crystal.I referred to a book called ”sekka-zusetsu” or "雪華図説" which means an illustrated explanation about snow crystals.This book was published in 1832 (天保3年) or Edo period.For more about "雪華図説",see here:dl.ndl.go.jp/info:ndljp/pid/2536975
Source Yamachem
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
You could get a bit dizzy from this one, but it might come in handy.
Source Dertig Media
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso