Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
The image depicts a seamless pattern of a tortoise in tortoiseshell (hexagon).
Source Yamachem
It looks very nice I think.
Source V. Hartikainen
A brown seamless wood texture in a form of stripe pattern. The result has turned out pretty well, in my opinion.
Source V. Hartikainen
A seamless texture of a rough concrete surface.
Source V. Hartikainen
The act or state of corrugating or of being corrugated, a wrinkle; fold; furrow; ridge.
Source Anna Litvinuk
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Derived from a drawing in 'Elfrica. An historical romance of the twelfth century', Charlotte Boger, 1885
Source Firkin
Here's a subtle marble-like background for use on websites.
Source V. Hartikainen
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
This white background pattern has a seamless grunge style texture. Here's a white grunge style background pattern. Use it as a tiled background image on web sites or for other purposes.
Source V. Hartikainen
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
More tactile goodness. This time in the form of some rough cloth.
Source Bartosz Kaszubowski
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
The image depicts a seamless pattern of pine tree leaves.
Source Yamachem
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
This is a seamless pattern which is derived from a flower petal image.
Source Yamachem
Used the 6th circle pattern designed by Viscious-Speed to create a print that can be used for card making or scrapbooking. Save as a PDF file for the best printing option.
Source Lovinglf
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
The perfect pattern for all your blogs about type, or type-related matters.
Source Atle Mo
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc