A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
Zero CC tileable bark texture, photographed and made by me. CC0
Source Sojan Janso
First pattern tailor-made for Retina, with many more to come. All the old ones are upscaled, in case you want to re-download.
Source Atle Mo
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A grayscale fabric pattern with vertical lines of stitch holes.
Source V. Hartikainen
Remixed from a drawing in 'Очерки Русской Исторіи въ памятникахъ быта', Petr Polevoi, 1879.
Source Firkin
A version without colours blended together to give a different look.
Source Firkin
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Remixed from a drawing that was uploaded to Pixabay by DavidZydd
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A very slick dark rubber grip pattern, sort of like the grip on a camera.
Source Sinisha
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
Zero CC tileable pine bark texture, photographed and made by me. CC0
Source Sojan Janso
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
This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!
Source V. Hartikainen
Fix and cc0 to get the tile this is based on.
Source SliverKnight
A pale yellow background pattern with vertical stripes. The stripes are partially faded. I think this background image turned out pretty well, especially those faded stripes.
Source V. Hartikainen
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin