I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
The image depicts the Japanese Edo pattern called "seigaiha" or "青海波" meaning "blue -sea- wave".I hope it's suitable for the summer season.
Source Yamachem
This was formed by distorting an image of a background on Pixabay.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
A large (588x375px) sand-colored pattern for your ever-growing collection. Shrink at will.
Source Alex Tapein
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Not the Rebel alliance, but a dark textured pattern.
Source Hendrik Lammers
Derived from elements found in a floral ornament drawing on Pixabay.
Source Firkin
Heavily remixed from a drawing in 'Barbara Leybourne; a story of eighty years ago', Sarah Hamer, 1889.
Source Firkin
A repeating background with dark brown stone-like texture and abstract pattern that looks like tree trunks.
Source V. Hartikainen
As simple and subtle as it gets. But sometimes that’s just what you want.
Source Designova
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel
Looks like an old wall. I guess that’s it then?
Source Viahorizon
This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
The image is a remix of "edo pattern-samekomon".I changed the color of dots from black to white and added BG in light-brown.
Source Yamachem
You know you can’t get enough of these linen-fabric-y patterns.
Source James Basoo
A free seamless background image with a texture of dark red "canvas". It should look very nice on web sites.
Source V. Hartikainen
From a drawing in 'Hubert Montreuil, or the Huguenot and the Dragoon', Francisca Ouvry, 1873.
Source Firkin
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
A re-make of the Gradient Squares pattern.
Source Dimitar Karaytchev
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
Retro Circles Background 4 No Black
Source GDJ