Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel
It’s an egg, in the form of a pattern. This really is 2012.
Source Paul Phönixweiß
Redrawn based on a drawing in 'По Сѣверо-Западу Россіи' Konstantin Sluchevsky, 1897.
Source Firkin
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
Prismatic Hypnotic Pattern No Background
Source GDJ
A set of paper filters. The base texture is generated the same way, only the compositing mode is varied.
Source Lazur URH
Prismatic Curved Diamond Pattern 8 No Background
Source GDJ
Has nothing to do with toast, but it’s nice and subtle.
Source Pippin Lee
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
Not the most creative name, but it’s a good all-purpose light background.
Source Dmitry
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Remixed from a drawing in 'Line and form", Walter Crane, 1914.
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