A repeating gloomy background image. This one consists of a pattern of black chains layered on top of a dark textured background.
Source V. Hartikainen
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
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
The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Background pattern made in "Grunge-Like" style. Available in both SVG and JPG formats. Edit to your needs then click the download button.
Source V. Hartikainen
Different from the original in being a simple tile stored as a pattern definition, rather than numerous repeated objects. Hence easy and quick to give this pattern to objects of different shapes. To get the tile in Inkscape, select the rectangle and use shift+alt+i.
Source Firkin
More in the paper realm, this time with fibers.
Source Jorge Fuentes
Sharp diamond pattern. A small 24x18px tile.
Source Tom Neal
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
Colorful Floral Background 3 No Black
Source GDJ
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Sort of like the Photoshop transparent background, but better!
Source Alex Parker