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. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Rounded Squares Grid 4 No Background
Source GDJ
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Inspired by a JPG that was uploaded to Pixabay by kokon_art
Source Firkin
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Everyone loves a diamond, right? Make your site sparkle.
Source AJ Troxell
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
A free background tile with a pattern of pink bump dots. This background tile is sweet! Moreover, it's designed for use as website backgrounds.
Source V. Hartikainen
It was called Navy Blue, but I made it dark. You know, the way I like it.
Source Ethan Hamilton
Psychedelic Geometric Background No Black
Source GDJ
This seamless pattern consists of a blue grid on a yellow background.
Source V. Hartikainen
Non-seamless pattern drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo