Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A free pink background pattern.
Source V. Hartikainen
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
A light gray fabric pattern with faded vertical stripes.
Source V. Hartikainen
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
The tile this is based on was adapted from an image that was uploaded to Pixabay by frolicsomepl. It can be had in Inkscape by selecting the rectangle and using shift+alt+i
Source Firkin
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Black paper texture, based on two different images.
Source Atle Mo
Based from Design Kindle
A seamless background texture of old cardboard.
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Number five from the same submitter, makes my job easy.
Source Dima Shiper
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Here's a new gray "fabric" pattern. Use it as backgrounds for websites or for other purposes.
Source V. Hartikainen
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
All good things come in threes, so I give you the third in my little concrete wall series.
Source Atle Mo
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
Turn your site into a dragon with this great scale pattern.
Source Alex Parker