There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
A seamless pattern formed from a square tile based on a jpg on Pixabay. The tile can be retrieved by selecting the rectangle in Inkscape and using 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 a drawing that was uploaded to Pixabay by ractapopulous
Source Firkin
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
Here's an yet another background for websites, with a seamless texture of wood planks this time.
Source V. Hartikainen
Sharp diamond pattern. A small 24x18px tile.
Source Tom Neal
It’s like Shine Dotted’s sister, only rotated 45 degrees.
Source mediumidee
Here's a dark background pattern that contains a steel grid pattern as a texture. Use it as a website background or for other purposes. It's free!
Source V. Hartikainen
Dark blue concrete wall with some small dust spots.
Source Atle Mo
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
Bigger is better, right? So here you have some large carbon fiber.
Source Factorio.us Collective
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Psychedelic Geometric Background No Black
Source GDJ
A seamless pattern formed from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Sharp pixel pattern, just like the good old days.
Source Paridhi
Seamless Background For Websites. It has a texture similar to cork-board.
Source V. Hartikainen