A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
You know you can’t get enough of these linen-fabric-y patterns.
Source James Basoo
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
This background pattern contains a seamless texture of bark. It's not very realistic, but I think it looks quite nice.
Source V. Hartikainen
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 Groovy Concentric Background 5
Source GDJ
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
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
This one looks like a cork panel. Feel free to use it as a tiled background on your blog or website.
Source V. Hartikainen
The image is a seamless pattern which is derived from a vine .Consequently, the vine got like dots via vectorization.The original vine is here:jp.pinterest.com/pin/500744052301410188/
Source Yamachem
A comeback for you: the popular Escheresque, now in black.
Source Patten
From a drawing in 'La Principauté de Liège et les Pays-Bas au XVIe siècle', Société des Bibliophiles Liégeois ,1887.
Source Firkin
A seamless web texture of "green stone".
Source V. Hartikainen
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
Remixed from a drawing in 'Очерки Русской Исторіи въ памятникахъ быта', Petr Polevoi, 1879.
Source Firkin
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
A free seamless background pattern for use on websites.
Source V. Hartikainen
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
I scanned a paper coffee cup. You know, in case you need it.
Source Atle Mo
Detailed but still subtle and quite original. Lovely gray shades.
Source Kim Ruddock
Lovely pattern with some good-looking non-random noise lines.
Source Zucx
Simple combination of stripy squares with their negatively coloured counterparts
Source Firkin
From a drawing in 'Studies for Stories', Jean Ingelow, 1864.
Source Firkin