A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
From a drawing in 'Danmarks Riges Historie af J. Steenstrup, Kr. Erslev, A. Heise, V. Mollerup, J. A. Fridericia, E. Holm, A. D. Jørgensen', 1897.
Source Firkin
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Fake or not, it’s quite luxurious.
Source Factorio.us Collective
Zero CC tileable Crackled Cement (streaks) texture, photographed and made by me. CC0
Source Sojan Janso
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
It’s an egg, in the form of a pattern. This really is 2012.
Source Paul Phönixweiß
Seamless pattern made from a tile that can be obtained in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A car pattern?! Can it be subtle? I say yes!
Source Radosław Rzepecki
Thin lines, noise and texture creates this crisp dark denim pattern.
Source Marco Slooten
Same classic 45-degree pattern, dark version.
Source Luke McDonald
The image is a seamless pattern of a fishnet.
Source Yamachem
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
Black And White Floral Pattern Background from PDP.
Source GDJ
Embossed lines and squares with subtle highlights.
Source Alex Parker
Colour version of the original pattern.
Source Firkin
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
Remixed from a drawing in 'Jezebel's Daughter', Wilkie Collins 1880
Source Firkin