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
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
This reminds me of Game Cube. A nice light 3D cube pattern.
Source Sander Ottens
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
Did anyone say The Hoff? This pattern is in no way related to Baywatch.
Source Josh Green
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
In the spirit of WWDC 2011, here is a dark iOS inspired linen pattern.
Source Atle Mo
Inspired by a 1930s wallpaper pattern I saw on TV.
Source Firkin
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Prismatic Abstract Line Art Pattern Background 2
Source GDJ
A brown seamless wood texture in a form of stripe pattern. The result has turned out pretty well, in my opinion.
Source V. Hartikainen
Inspired by a drawing in 'Kulturgeschichte', Freidrich Hellwald, 1896.
Source Firkin
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
One can never have too few rice paper patterns, so here is one more.
Source Atle Mo
A comeback for you: the popular Escheresque, now in black.
Source Patten
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen