A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
This one needs to be used in small areas; you can see it repeat.
Source Luca
A seamless background of warped stripes on paper.
Source V. Hartikainen
Colourful background achieved with gradient fills.
Source Firkin
Remixed from a drawing in 'Incidents on a Journey through Nubia to Darfoor', F. Ensor, 1891.
Source Firkin
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
Turn your site into a dragon with this great scale pattern.
Source Alex Parker
Prismatic Groovy Concentric Background
Source GDJ
This pattern comes in orange, and it looks as if it is "made of glass".
Source V. Hartikainen
A seamless pattern recreated from an image on Pixabay. It is reminiscent of parquet flooring and is formed from a square tile, which can be recovered in Inkscape by selecting the ungrouped rectangle and using shift-alt-I together.
Source Firkin
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
A seamless textured paper for backgrounds. Colored in pale orange hues.
Source V. Hartikainen
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
This light blue background pattern is quite pleasing to the eye, it consists of a tiny rough grid pattern, which is seamless by design. That's it, if you like the color, you can use this seamless pattern in a web design without making any further modifications to it.
Source V. Hartikainen