This one is something special. I’d call it a flat pattern, too. Very well done, sir!
Source GetDiscount
Prismatic Hypnotic Pattern No Background
Source GDJ
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
This ladies and gentlemen, is texturetastic! Love it.
Source Adam Pickering
Derived from an image that was uploaded to Pixabay by pugmom40
Source Firkin
Sounds like something from World of Warcraft. Has to be good.
Source Tony Kinard
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
You could get a bit dizzy from this one, but it might come in handy.
Source Dertig Media
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
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
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein