Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
Prismatic Groovy Concentric Background 4
Source GDJ
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Plywood Web Background background image for use in web design.
Source V. Hartikainen
This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
A dark background pattern/texture of a dimpled metal plate.
Source V. Hartikainen
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
Prismatic Polyskelion Pattern No Background
Source GDJ
Derived from a JPG that was uploaded to Pixabay by ractapopulous
Source Firkin
Classic 45-degree pattern, light version.
Source Luke McDonald
This one has rusty dark brown texture.
Source V. Hartikainen
Nicely executed tiling for an interesting pattern.
Source Ignasi Àvila Padró
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
Prismatic Basic Pattern 2 No Background
Source GDJ
From a drawing in 'Real Sailor-Songs', John Ashton, 1891.
Source Firkin
Luxurious looking pattern (for a T-shirt maybe?) with a hint of green.
Source Simon Meek
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
Prismatic Snowflakes Pattern No Background
Source GDJ