Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Here's a new gray "fabric" pattern. Use it as backgrounds for websites or for other purposes.
Source V. Hartikainen
A free seamless background texture that looks like a brown stone wall.
Source V. Hartikainen
ZeroCC tileable wood boards texture, photographed and made by me. CC0
Source Sojan Janso
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
8 by 8 pixels, and just what the title says.
Source pixilated
Inspired by the B&O Play, I had to make this pattern.
Source Atle Mo
Retro Circles Background 8 No Black
Source GDJ
Pattern formed from simple shapes. Black version.
Source Firkin
Number five from the same submitter, makes my job easy.
Source Dima Shiper
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Looks as if it's spray painted on the wall. You can be sure that this pattern will seamlessly fill your backgrounds on web pages.
Source V. Hartikainen
It’s an egg, in the form of a pattern. This really is 2012.
Source Paul Phönixweiß
Prismatic Abstract Background Design No Black
Source GDJ
This one is amazing, truly original. Go use it!
Source Viahorizon
Prismatic Geometric Tessellation Pattern No Background
Source GDJ
You know you can’t get enough of these linen-fabric-y patterns.
Source James Basoo
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin