Not so subtle. These tileable wood patterns are very useful.
Source Elemis
From a drawing in 'Studies for Stories', Jean Ingelow, 1864.
Source Firkin
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
Just the symbols of the signs of the zodiac distributed in a chequer board-like pattern
Source Firkin
A seamless pattern formed from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
The original enhanced with some gradients.
Source Firkin