This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Prismatic Abstract Geometric Background 4
Source GDJ
There are many carbon patterns, but this one is tiny.
Source Designova
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
A seamless web texture of "green stone".
Source V. Hartikainen
A comeback for you: the popular Escheresque, now in black.
Source Patten
Prismatic Snowflakes Pattern 2 No Background
Source GDJ
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A colourful background drawn originally in paint.net and vectorised in Vector Magic.
Source Firkin
Prismatic Abstract Background Design
Source GDJ
Prismatic Geometric Tessellation Pattern 2 No Background
Source GDJ
From a drawing in 'Prose and Verse ', William Linton, 1836.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Looks like an old wall. I guess that’s it then?
Source Viahorizon
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo
Remixed from a drawing in 'Incidents on a Journey through Nubia to Darfoor', F. Ensor, 1891.
Source Firkin
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Prismatic Hypnotic Pattern 2 No Background
Source GDJ
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib