Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Zero CC tileable ground (#2) cracked, crackled texture, made by me. CC0
Source Sojan Janso
No idea what Nistri means, but it’s a crisp little pattern nonetheless.
Source Markus Reiter
A nice one indeed, but I have a feeling we have it already? If you spot a copy, let me know on Twitter.
Source Graphiste
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
This light blue background pattern is quite pleasing to the eye, it consists of a tiny rough grid pattern, which is seamless by design. That's it, if you like the color, you can use this seamless pattern in a web design without making any further modifications to it.
Source V. Hartikainen
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
Not the Rebel alliance, but a dark textured pattern.
Source Hendrik Lammers
Lovely pattern with splattered vintage speckles.
Source David Pomfret
From a drawing in 'Cowdray: the history of a great English House', Julia Roundell, 1884.
Source Firkin
The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin