Not so subtle. These tileable wood patterns are very useful.
Source Elemis
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
ZeroCC tileable moss texture, photographed and made by me. CC0
Source Sojan Janso
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Retro Circles Background 8 No Black
Source GDJ
A background pattern with blue on white vertical stripes.
Source V. Hartikainen
Prismatic Polyskelion Pattern No Background
Source GDJ
Prismatic Abstract Background Design
Source GDJ
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
More carbon fiber for your collections. This time in white or semi-dark gray.
Source Badhon Ebrahim
Washi (和紙?) is a type of paper made in Japan. Here’s the pattern for you!
Source Carolynne
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Farmer could be some sort of fabric pattern, with a hint of green.
Source Fabian Schultz
It’s okay to be square! A nice light gray pattern with random squares.
Source Waseem Dahman
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
Zero CC tileable hard cover green book, scanned and made by me. CC0
Source Sojan Janso
More leather, and this time it’s bigger! You know, in case you need that.
Source Elemis
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The image depicts a seamless pattern of a Japanese family crest called "chidori" in Japanese .A chidori in Japanese means a plover in English.
Source Yamachem
Fix and cc0 to get the tile this is based on.
Source SliverKnight
A free background image with a seamless texture of cardboard. This texture of cardboard looks quite realistic, especially when is actually tiled.
Source V. Hartikainen
Prismatic Rounded Squares Grid 4 No Background
Source GDJ