A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
An abstract texture of black metal pipes (seamless).
Source V. Hartikainen
From a drawing in 'From Snowdon to the Sea. Striking stories of North and South Wales', Marie Trevelyan, 1895.
Source Firkin
It looks very nice I think.
Source V. Hartikainen
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
A nice and simple gray stucco material. Great on its own, or as a base for a new pattern.
Source Bartosz Kaszubowski
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
It’s okay to be square! A nice light gray pattern with random squares.
Source Waseem Dahman
Number 3 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
A seamless pattern formed from a modified version of rwwgub's tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
I skipped number 3, because it wasn’t all that great. Sorry.
Source Dima Shiper
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
It’s a hole, in a pattern. On your website. Dig it!
Source Josh Green
Seamless pattern the basic tile for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
Just like your old suit, all striped and smooth.
Source Alex Berkowitz
Have you wondered about how it feels to be buried alive? Here is the pattern for it.
Source Hendrik Lammers
A hint of orange color, and some crossed and embossed lines.
Source Adam Anlauf
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Has nothing to do with toast, but it’s nice and subtle.
Source Pippin Lee
A repeating background with seamless texture of stone. There haven't been any stone-like backgrounds for a while, so I have decided to create one more. The rest can be found in the appropriate category.
Source V. Hartikainen