A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
From a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Prismatic Polka Dots Mark II No Background
Source GDJ
The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
CC0 and seamless wellington boot pattern.
Source SliverKnight
8 by 8 pixels, and just what the title says.
Source pixilated
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
A seamless background pattern of dark brown wood planks.
Source V. Hartikainen
Colorful Floral Background 3 No Black
Source GDJ
Little x’es, noise and all the stuff you like. Dark like a Monday, with a hint of blue.
Source Tom McArdle
I’m guessing this is related to the Sony Vaio? It’s a nice pattern no matter where it’s from.
Source Zigzain
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin