If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
This is a seamless pattern which is derived from a flower petal image.
Source Yamachem
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
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
This one is amazing, truly original. Go use it!
Source Viahorizon
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
Remixed from a raster on Pixabay, that was uploaded by ArtsyBee.
Source Firkin
Lovely pattern with some good-looking non-random noise lines.
Source Zucx
Zero CC tileable wood texture, made by me procedurally in Neo Texture Edit.
Source Sojan Janso
From a drawing in 'Hubert Montreuil, or the Huguenot and the Dragoon', Francisca Ouvry, 1873.
Source Firkin
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
Same as the black version, but now in shades of gray. Very subtle and fine grained.
Source Atle Mo
Adapted from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
Seamless Light Background Texture.
Source V. Hartikainen
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
The image depicts a seamless pattern of a tortoise in tortoiseshell (hexagon).
Source Yamachem
Zero CC tileable bark texture, photographed and made by me. CC0
Source Sojan Janso
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin