Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Retro Circles Background 8 No Black
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Vertical lines with a bumpy, yet crisp, feel to it.
Source Raasa
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Otis Ray Redding was an American soul singer-songwriter, record producer, arranger, and talent scout. So you know.
Source Thomas Myrman
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
I guess this is inspired by the city of Ravenna in Italy and its stone walls.
Source Sentel
A version without colours blended together to give a different look.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
You know I’m a sucker for these. Well-crafted paper pattern.
Source Mihaela Hinayon
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
A fun-looking elastoplast/band-aid pattern. A hint of orange tone in this one.
Source Josh Green
Heavily remixed from a drawing that was uploaded to Pixabay by ractapopulous
Source Firkin
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
It’s an egg, in the form of a pattern. This really is 2012.
Source Paul Phönixweiß
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin