A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
It’s big, it’s gradient—and it’s square.
Source Brankic1979
Gold Triangular Seamless Pattern No Background
Source GDJ
Retro Circles Background 5 No Black
Source GDJ
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A pattern drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
Prismatic Abstract Geometric Background 4
Source GDJ
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
Black brick wall pattern. Brick your site up!
Source Alex Parker
A version without colours blended together to give a different look.
Source Firkin
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Utilising a bird from s-light and some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
This was formed by distorting an image of a background on Pixabay.
Source Firkin
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
Hey, you never know when you’ll need a bird pattern, right?
Source Pete Fecteau
Zero CC tileable dry grass texture, photographed and made by me. CC0
Source Sojan Janso
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin