Might not be super subtle, but quite original in its form.
Source Alex Smith
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo
Classic vertical lines, in all its subtlety.
Source Cody L
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
Prismatic Triangular Background Design Mark II 5
Source GDJ
This seamless web background texture looks like gray stone. It's great for using as a background image on web pages, or on some of their elements. Anyway, I hope you will find use for it.
Source V. Hartikainen
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Just like your old suit, all striped and smooth.
Source Alex Berkowitz
Prismatic Curved Diamond Pattern 6 No Background
Source GDJ
Thin lines, noise and texture creates this crisp dark denim pattern.
Source Marco Slooten
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
Dark Tile-able Grunge Texture. I think this texture can be classified as grunge. It's free and seamless, as always.
Source V. Hartikainen
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
One more sharp little tile for you. Subtle circles this time.
Source Blunia
This is a remix of "geometrical pattern 01".
Source Yamachem
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Geometric lines are always hot, and this pattern is no exception.
Source Listvetra