Because I love dark patterns, here is Brushed Alum in a dark coating.
Source Tim Ward
A seamless pattern with wide vertical stripes colored in pale yellow.
Source V. Hartikainen
Square design drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
Might not be super subtle, but quite original in its form.
Source Alex Smith
The tile this is formed from can be retrieved in Inkscape by selecting the rectangle and using shift+alt+i
Source Firkin
Background Wall, Art Abstract, Watercolor Vintage style CC0 texture.
Source Ractapopulous
With a name this awesome, how can I go wrong?
Source Nikolay Boltachev
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
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
Here's an yet another background for websites, with a seamless texture of wood planks this time.
Source V. Hartikainen