CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Seamless Dark Grunge Texture. Here's a new grunge texture for use as a background.
Source V. Hartikainen
The image depicts a seamless pattern made using a bird's face.
Source Yamachem
Background formed from the iconic plastic construction bricks that gave me endless hours of fun when I was a lad.
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
More leather, and this time it’s bigger! You know, in case you need that.
Source Elemis
You know you can’t get enough of these linen-fabric-y patterns.
Source James Basoo
A seamless pattern with wide vertical stripes colored in pale yellow.
Source V. Hartikainen
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
Prismatic Abstract Geometric Background 2
Source GDJ
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
If you don’t like cream and pixels, you’re in the wrong place.
Source Mizanur Rahman
Derived from a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin