This one is amazing, truly original. Go use it!
Source Viahorizon
A seamless pattern made from the gold Penrose triangle by GDJ and the two remixes
Source Firkin
This tiled background comes in red and consists of tiles that look like gemstones. It is more for blogs or social profiles, I think.
Source V. Hartikainen
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
Bright Multicolored Floral Background by Karen Arnold from PDP.
Source GDJ
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
Geometric lines are always hot, and this pattern is no exception.
Source Listvetra
Colored maple leaves scattered on a surface. This is tileable, so it can be used as a background or wallpaper.
Source Eady
Inspired by a design found in 'Konstantinápolyi emlékeim', Miklos Chriszto, 1893.
Source Firkin
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
Little x’es, noise and all the stuff you like. Dark like a Monday, with a hint of blue.
Source Tom McArdle
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This texture looks like old leather. It should look great as a background on web pages.
Source V. Hartikainen
From a drawing in 'Studies for Stories', Jean Ingelow, 1864.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Prepared mostly as a raster in Paint.net and vectorised.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A seamless background tile of aged paper with shabby look.
Source V. Hartikainen