Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
A hint of orange color, and some crossed and embossed lines.
Source Adam Anlauf
The file was named striped lens, but hey – Translucent Fibres works too.
Source Angelica
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Derived from a design in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
Produced using the clouds, flames and glass blocks plug-ins in Paint.net and the resulting .PNG vectorised with Vector Magic.
Source Firkin
A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
Inspired by a design found in 'Konstantinápolyi emlékeim', Miklos Chriszto, 1893.
Source Firkin
Submitted in a cream color, but you know how I like it.
Source Devin Holmes
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Very simple, very blu(e). Subtle and nice.
Source Seb Jachec
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
8 by 8 pixels, and just what the title says.
Source pixilated
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
Prismatic Abstract Background Design No Black
Source GDJ