The following repeating website background is colored in a blue gray color and resembles a concrete wall or something similar to it.
Source V. Hartikainen
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
White circles connecting on a light gray background.
Source Mark Collins
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
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
A seamless pattern with a unit cell drawn as a bitmap in Paint.net and vectorized in Vector Magic.
Source Firkin
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
An abstract pale yellow paper-like background with stains colored in yellow and green.
Source V. Hartikainen
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Black And White Floral Pattern Background from PDP.
Source GDJ
A seamless pattern formed from a modified version of rwwgub's tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
A textured blue background pattern with vertical stripes.
Source V. Hartikainen
Colour version of the original pattern.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin