A comeback for you: the popular Escheresque, now in black.
Source Patten
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
Sharp pixel pattern looking like some sort of fabric.
Source Dmitry
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
A dark striped seamless pattern suitable for use as a background on websites.
Source V. Hartikainen
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
Number 5 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Light gray grunge wall with a nice texture overlay.
Source Adam Anlauf
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Hey, you never know when you’ll need a bird pattern, right?
Source Pete Fecteau
From a drawing in 'Danmarks Riges Historie af J. Steenstrup, Kr. Erslev, A. Heise, V. Mollerup, J. A. Fridericia, E. Holm, A. D. Jørgensen', 1897.
Source Firkin
A rusty grunge background for websites. Feel free to use it in your site's theme.
Source V. Hartikainen
An abstract Background pattern of purple twisty patterns.
Source TikiGiki
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
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
A pattern derived from repeating unit cells each derived from part of a mosaic in paint.net. The starting point for the mosaic was a picture of some prawns!
Source Firkin
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
A floral background formed from numerous clones of flower 117.
Source Firkin