A pattern drawn in Paint.net and vectorized in Inkscape.
Source Firkin
A seamless background tile of aged paper with shabby look.
Source V. Hartikainen
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
Original seamless pattern with an Inkscape filter.
Source Firkin
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Dark blue concrete wall with some small dust spots.
Source Atle Mo
Classic 45-degree pattern, light version.
Source Luke McDonald
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
You can never get enough of these tiny pixel patterns with sharp lines.
Source Designova
Remixed from a drawing in 'Очерки Русской Исторіи въ памятникахъ быта', Petr Polevoi, 1879.
Source Firkin
A blue gray fabric-like texture for websites. An yet another fabric-like texture. It has subtle vertical and diagonal stripes to it.
Source V. Hartikainen
A version without colours blended together to give a different look.
Source Firkin
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
8 by 8 pixels, and just what the title says.
Source pixilated