CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
A nice looking light gray background pattern with diagonal stripes.
Source V. Hartikainen
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
From a drawing in 'Prose and Verse ', William Linton, 1836.
Source Firkin
The image is a remix of "edo pattern-samekomon".I changed the color of dots from black to white and added BG in light-yellow.
Source Yamachem
The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Prismatic Groovy Concentric Background 2
Source GDJ
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
A seamless stone-like background for blogs or any other type of websites.
Source V. Hartikainen
Traced from a drawing in 'Household Stories from the Collection of the Brothers Grimm', Wilhelm Carl Grimm , 1882.
Source Firkin
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
On a large canvas you can see it tiling, but used on smaller areas, it’s beautiful.
Source Paul Phönixweiß
An emulated “transparent” background pattern, like that of all kinds of computer graphics software.
Source AdamStanislav
I love the movie Pineapple Express, and I’m also liking this Pineapple right here.
Source Audee Mirza
This reminds me of Game Cube. A nice light 3D cube pattern.
Source Sander Ottens
Might not be super subtle, but quite original in its form.
Source Alex Smith