Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
A seamless pattern the starting point for which was a 'light rays' rendering in Paint.net.
Source Firkin
Hexagonal dark 3D pattern. What more can you ask for?
Source Norbert Levajsics
U.S.-based National Fire Protection Association standard fire diamond for flagging risks posed by hazardous materials. The red diamond has a number 0-4 depending on flammability. The blue diamond has a number 0-4 depending on health hazard. The yellow has a number 0-4 depending on reactivity. the white square has a special notice, e.g OX for oxidizer.
Source Firkin
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
This metal background pattern resembles a metal plate with rivets. Solid rivets on a metal plate.
Source V. Hartikainen
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
A brown metallic grid pattern layered on top of a dark fabric texture. It should look great when using as a tiled background on web pages, especially blogs.
Source V. Hartikainen
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
This one is super crisp at 2X. Lined paper with some dust and scratches.
Source HQvectors
Pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin
There are many carbon patterns, but this one is tiny.
Source Designova
It’s okay to be square! A nice light gray pattern with random squares.
Source Waseem Dahman
This pattern comes in orange, and it looks as if it is "made of glass".
Source V. Hartikainen
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
Free tiled background with colorful stripes and white splatter.
Source V. Hartikainen
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A seamless pale yellow paper background with a pattern of animal tracks.
Source V. Hartikainen
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim