Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Prismatic Polka Dots Mark II No Background
Source GDJ
A pattern drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
This beige background pattern resembles a concrete wall with engravings or something similar to it.
Source V. Hartikainen
Prismatic Chevrons Pattern 5 With Background
Source GDJ
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Snowflakes Pattern No Background
Source GDJ
The following orange background pattern resembles a honeycomb.
Source V. Hartikainen
Prismatic Polka Dots 3 No Background
Source GDJ
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Fake or not, it’s quite luxurious.
Source Factorio.us Collective
Prismatic Abstract Background Design
Source GDJ
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss