A seamlessly tile-able grunge background image.
Source V. Hartikainen
A cute x, if you need that sort of thing.
Source Juan Scrocchi
Bigger is better, right? So here you have some large carbon fiber.
Source Factorio.us Collective
Oh yes, it happened! A pattern in full color.
Source Atle Mo
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
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
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
This yellow background consists of a pattern of glossy gold buttons arranged in polka dot style on a seamless texture. Here's a pale yellow background pattern. Feel free to use it for your needs!
Source V. Hartikainen
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Same as Silver Scales, but in black. Turn your site into a dragon with this great scale pattern.
Source Alex Parker
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
The image depicts an edo-era pattern called "same-komon" or "鮫小紋"which looks like a shark skin.The "same" in Japanese means shark in English.
Source Yamachem
Prismatic Geometric Pattern Background
Source GDJ
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
Clean and crisp lines all over the place. Wrap it up with this one.
Source Dax Kieran
Nice little grid. Would work great as a base on top of some other patterns.
Source Arno Gregorian
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin