A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
From a drawing in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
Prismatic Abstract Line Art Pattern Background
Source GDJ
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
A pattern drawn in Paint.net and vectorized in Inkscape.
Source Firkin
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
The tile this fill pattern is based on can be had by using shift+alt+i on the rectangle.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
Dark pattern with some nice diagonal stitched lines crossing over.
Source Ashton
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'Hundert Jahre in Wort und Bild', S. Stefan, 1899.
Source Firkin
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay
Submitted as a black pattern, I made it light and a few steps more subtle.
Source Andy