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
First pattern tailor-made for Retina, with many more to come. All the old ones are upscaled, in case you want to re-download.
Source Atle Mo
A series of 5 patterns. That’s what the P stands for, if you didn’t guess it.
Source Dima Shiper
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A large (588x375px) sand-colored pattern for your ever-growing collection. Shrink at will.
Source Alex Tapein
I’m starting to think I have a concrete wall fetish.
Source Atle Mo
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Like the name suggests, this background image consists of a pattern of dark bricks. It may be an option for you, if you are looking for something that looks like a brick wall for use as a background on web pages. It's not a masterpiece, but looks pretty nice when is tiled.
Source V. Hartikainen
A textured orange background pattern with vertical stripes.
Source V. Hartikainen
A light background pattern with diagonal stripes. Here's a simple light striped background for you.
Source V. Hartikainen
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
A seamlessly tile-able grunge background image.
Source V. Hartikainen
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
The file was named striped lens, but hey – Translucent Fibres works too.
Source Angelica
A repeating background with wood/straw like texture.
Source V. Hartikainen
Here's a subtle marble-like background for use on websites.
Source V. Hartikainen
Used correctly, this could be nice. Used in a bad way, all hell will break loose.
Source Atle Mo
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight