Inspired by an image that was uploaded to Pixabay by geralt
Source Firkin
Like the name suggests, this background image consists of a pattern of dark bricks. It may be an option for you, if you are looking for something that looks like a brick wall for use as a background on web pages. It's not a masterpiece, but looks pretty nice when is tiled.
Source V. Hartikainen
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Green Background Pattern
Source V. Hartikainen
Prismatic Polka Dots 3 No Background
Source GDJ
An interesting dark spotted pattern at an angle.
Source Hendrik Lammers
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
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
Seamless tile drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Pattern produced in Paint.net using the Vibrato plug-in.
Source Firkin
Background pattern originally a PNG drawn in Paint.net
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Nice little grid. Would work great as a base on top of some other patterns.
Source Arno Gregorian