A seamless pattern formed from a square tile based on a jpg on Pixabay. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Farmer could be some sort of fabric pattern, with a hint of green.
Source Fabian Schultz
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
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Prismatic Snowflakes Pattern 2 No Background
Source GDJ
Use shift+alt+i on the selected rectangle in Inkscape to get the tile this is based on
Source Firkin
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
Remixed from a drawing in 'Hungary. A guide book. By several authors', 1890.
Source Firkin
Prismatic Polka Dots Mark II 3 No Background
Source GDJ
Remixed from a raster on Pixabay that was uploaded by ArtsyBee.
Source Firkin
This seamless web background texture looks like gray stone. It's great for using as a background image on web pages, or on some of their elements. Anyway, I hope you will find use for it.
Source V. Hartikainen
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
A pattern formed from a photograph of a 16th century ceramic tile.
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A white version of the very popular linen pattern.
Source Ant Ekşiler
Prismatic Groovy Concentric Background 4
Source GDJ
A comeback for you: the popular Escheresque, now in black.
Source Patten
A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
Number 1 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel