Sometimes you just need the simplest thing.
Source Fabricio
There are many carbon patterns, but this one is tiny.
Source Designova
From an image on opengameart.org shared by rubberduck.
Source Firkin
An alternative colour scheme to the original seamless pattern.
Source Firkin
Inspired by a pattern found in 'A General History of Hampshire, or the County of Southampton, including the Isle of Wight', Bernard Woodwood, 1861
Source Firkin
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
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
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
This is lovely, just the right amount of subtle noise, lines and textures.
Source Richard Tabor
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Alternative colour scheme to the original.
Source Firkin
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
A seamless pattern formed from a tile made from page ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Everyone loves a diamond, right? Make your site sparkle.
Source AJ Troxell
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A repeating background of beige paper with vintage look. Repeats to infinity, as usual.
Source V. Hartikainen
Background formed from the original with an emboss effect.
Source Firkin