Lovely pattern with some good-looking non-random noise lines.
Source Zucx
This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!
Source V. Hartikainen
The image depicts a seamless pattern made using a bird's face.
Source Yamachem
Another fairly simple design drawn in Paint.net and vectorized in Inkscape.
Source Firkin
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
A repeating background with dark brown stone-like texture and abstract pattern that looks like tree trunks.
Source V. Hartikainen
A car pattern?! Can it be subtle? I say yes!
Source Radosław Rzepecki
Remixed from a drawing in 'An Index to Deering's Nottinghamia Vetus et Nova', Rupert Chicken, 1899. The unit tile can be had by selecting the rectangle in Inkscape and using shift-alt-i
Source Firkin
Tiny, tiny 3D cubes. Reminds me of the good old pattern from k10k.
Source Etienne Rallion
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A seamless pattern based on a tile that can be achieved 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
Classic 45-degree pattern, light version.
Source Luke McDonald
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
From a drawing in 'Real Sailor-Songs', John Ashton, 1891.
Source Firkin
First pattern tailor-made for Retina, with many more to come. All the old ones are upscaled, in case you want to re-download.
Source Atle Mo
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin