A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
Number 2 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
A seamless pattern based on a tile that can be achieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
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
ZeroCC tileable beechwood wood texture, generated in Neo Texture Edit by me. CC0
Source Sojan Janso
Pixel by pixel, sharp and clean. Very light pattern with clear lines.
Source M.Ashok
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Prismatic Abstract Geometric Background 5
Source GDJ
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran