The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
A very dark asfalt pattern based off of a photo taken with my iPhone.
Source Atle Mo
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
A seamless pattern formed from a modified version of rwwgub's tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Remixed from an image on Pixabay uploaded by Prawny
Source Firkin
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
This one is something special. I’d call it a flat pattern, too. Very well done, sir!
Source GetDiscount
I guess this is inspired by the city of Ravenna in Italy and its stone walls.
Source Sentel
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
Abstract Tiled Background Extended 10
Source GDJ
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
A free background tile with a pattern of pink bump dots. This background tile is sweet! Moreover, it's designed for use as website backgrounds.
Source V. Hartikainen