A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
Zero CC tileable bark texture, photographed and made by me. CC0
Source Sojan Janso
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Prismatic Abstract Geometric Background 4
Source GDJ
The original enhanced with one of Inkscapes's filters.
Source Firkin
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
This background has abstract texture with some similarities to wood.
Source V. Hartikainen
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.
Source Ivan Ginev
Square design drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
Prepared mostly as a raster in Paint.net and vectorised.
Source Firkin
An interesting dark spotted pattern at an angle.
Source Hendrik Lammers
A repeating background with seamless texture of stone. There haven't been any stone-like backgrounds for a while, so I have decided to create one more. The rest can be found in the appropriate category.
Source V. Hartikainen
A seamless marble-like texture colored in light blue.
Source V. Hartikainen
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin
Colorful Floral Background 3 No Black
Source GDJ
It was called Navy Blue, but I made it dark. You know, the way I like it.
Source Ethan Hamilton
Everyone loves a diamond, right? Make your site sparkle.
Source AJ Troxell
Continuing the geometric trend, here is one more.
Source Mike Warner
Sharp pixel pattern, just like the good old days.
Source Paridhi
This is a grid, only it’s noisy. You know. Reminds you of those printed grids you draw on.
Source Vectorpile
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin