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
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Semi-light fabric pattern made out of random pixels in shades of gray.
Source Atle Mo
CC0 remixed from a drawing. Walter Crane, 1914, Firkin.
Source SliverKnight
Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
Same classic 45-degree pattern, dark version.
Source Luke McDonald
Based on an image that was uploaded to Pixabay by devanath
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
Background formed from the original with an emboss effect
Source GDJ
Prismatic Abstract Background Design
Source GDJ
Colorful Floral Background No Black
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
This background pattern contains a texture of yellow wood planks. I think it looks quite original.
Source V. Hartikainen
You may use it as is, or modify it as you like.
Source V. Hartikainen
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
A pattern drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A seamless pattern recreated from an image on Pixabay. It is reminiscent of parquet flooring and is formed from a square tile, which can be recovered in Inkscape by selecting the ungrouped rectangle and using shift-alt-I together.
Source Firkin
It looks like a polished stone surface to me. Download it for free, as always.
Source V. Hartikainen