Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
A seamless pattern the starting point for which was a 'light rays' rendering in Paint.net.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
This texture looks like old leather. It should look great as a background on web pages.
Source V. Hartikainen
Here's a new gray "fabric" pattern. Use it as backgrounds for websites or for other purposes.
Source V. Hartikainen
No idea what Nistri means, but it’s a crisp little pattern nonetheless.
Source Markus Reiter
Gold Triangular Seamless Pattern No Background
Source GDJ
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