Not so subtle. These tileable wood patterns are very useful.
Source Elemis
This one needs to be used in small areas; you can see it repeat.
Source Luca
Submitted by DomainsInfo – wtf, right? But hey, a free pattern.
Source DomainsInfo
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
You may use it as is, or modify it as you like.
Source V. Hartikainen
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Seamless pattern formed from a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Did anyone say The Hoff? This pattern is in no way related to Baywatch.
Source Josh Green
This ons is quite old school looking. Retro, even. I like it.
Source Arno Declercq
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
I took the liberty of using Dmitry’s pattern and made a version without perforation.
Source Atle Mo
Remixed from an image on Pixabay, the original having been uploaded by darkmoon1968.
Source Firkin
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
It looks very nice I think.
Source V. Hartikainen