A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
Remixed from a drawing in 'Jezebel's Daughter', Wilkie Collins 1880
Source Firkin
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
Prismatic Hexagonalist Pattern No Background
Source GDJ
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin
Colour version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Light honeycomb pattern made up of the classic hexagon shape.
Source Federica Pelzel
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel
A brown seamless wood texture in a form of stripe pattern. The result has turned out pretty well, in my opinion.
Source V. Hartikainen
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
This one is something special. I’d call it a flat pattern, too. Very well done, sir!
Source GetDiscount
Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.
Source Ivan Ginev
From a drawing in 'Studies for Stories', Jean Ingelow, 1864.
Source Firkin
The image depicts a seamless pattern of a tortoise in tortoiseshell (hexagon).
Source Yamachem
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
This makes me wanna shoot some pool! Sweet green pool table pattern.
Source Caveman
Sharp pixel pattern, just like the good old days.
Source Paridhi
From a drawing in 'Cowdray: the history of a great English House', Julia Roundell, 1884.
Source Firkin