People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
A browner version of the original weathered fence texture.
Source Firkin
A seamless background colored in pale orange. It has a paper like texture with diagonal grid pattern.
Source V. Hartikainen
The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.
Source Nathan Spady
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
Prismatic Polka Dots 3 No Background
Source GDJ
An alternative colour scheme to the original seamless pattern.
Source Firkin
Your eyes can trip a bit from looking at this – use it wisely.
Source Michal Chovanec
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
From a drawing in 'A Rolling Stone. A tale of wrongs and revenge', John Hartley, 1878.
Source Firkin
A heavy dark gray base, some subtle noise and a 45-degree grid makes this look like a pattern with a tactile feel to it.
Source Atle Mo
This is a more minute version of "fishnet 01".The image depicts a seamless pattern of a fishnet with a plenty of fish.It may be a lucky charm for fishermen.
Source Yamachem
Tiny circle waves, almost like the ocean.
Source Sagive
Use shift+alt+i on the selected rectangle in Inkscape to get the tile this is based on
Source Firkin
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
The texture of this background image has some similarities with leather, and it's colored in a dark brown color. So, if you are looking for a dark brown background image for your website, this may be an option for you.
Source V. Hartikainen
No relation to the band, but damn it’s subtle!
Source Thomas Myrman
Black & white version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
ZeroCC tileable mossy (lichen) stone texture, edited from pixabay. CC0
Source Sojan Janso