A free seamless background texture that looks like a brown stone wall.
Source V. Hartikainen
This reminds me of Game Cube. A nice light 3D cube pattern.
Source Sander Ottens
ZeroCC tileable moss texture, photographed and made by me. CC0
Source Sojan Janso
From a drawing of the coat of arms of the Ottoman Empire on Wikimedia.
Source Firkin
Adapted from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Lovely pattern with some good-looking non-random noise lines.
Source Zucx
Seamless Olive Green Web Background Image
Source V. Hartikainen
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Prismatic Polka Dots Mark II No Background
Source GDJ
This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Prismatic Abstract Geometric Background 4
Source GDJ
Use shift+alt+i on the selected rectangle in Inkscape to get the tile this is based on
Source Firkin
Semi-light fabric pattern made out of random pixels in shades of gray.
Source Atle Mo
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
A seamless background tile of aged paper with shabby look.
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin
A seamless pattern formed from a modified version of rwwgub's tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin