Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
This seamless pattern consists of a blue grid on a yellow background.
Source V. Hartikainen
Here's a tile-able wood background image for use in web design.
Source V. Hartikainen
Looks like an old wall. I guess that’s it then?
Source Viahorizon
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A bit like some carbon, or knitted netting if you will.
Source Anna Litvinuk
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i
Source Firkin
From a drawing in 'A Life Interest', Mrs Alexander, 1888.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
Just what the name says, paper fibers. Always good to have.
Source Heliodor jalba
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A heavy hitter at 400x400px, but lovely still.
Source Breezi
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Prismatic Rounded Squares Grid 4 No Background
Source GDJ