Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Green Web Background, Seamless tile.
Source V. Hartikainen
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
Prismatic Abstract Background Design No Black
Source GDJ
This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!
Source V. Hartikainen
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Looks like an old wall. I guess that’s it then?
Source Viahorizon
Abstract Ellipses Background Grayscale
Source GDJ
Derived from a PNG that was uploaded to Pixabay by nutkitten
Source Firkin
Honestly, who does not like a little pipe and mustache?
Source Luca Errico
A seamless texture of worn out "cardboard".
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
No idea what Nistri means, but it’s a crisp little pattern nonetheless.
Source Markus Reiter
Seamless Light Background Texture.
Source V. Hartikainen
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Derived from a drawing in 'The Murmur of the Shells', Samuel Cowen, 1879.
Source Firkin
Tiny circle waves, almost like the ocean.
Source Sagive
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
You were craving more leather, so I whipped this up by scanning a leather jacket.
Source Atle Mo
Submitted in a cream color, but you know how I like it.
Source Devin Holmes