From a drawing in 'Studies for Stories', Jean Ingelow, 1864.
Source Firkin
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
There are many carbon patterns, but this one is tiny.
Source Designova
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A new one called white wall, not by me this time.
Source Yuji Honzawa
He influenced us all. “Don’t be sad because it’s over. Smile because it happened.”
Source Atle Mo
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
This tiled background comes in red and consists of tiles that look like gemstones. It is more for blogs or social profiles, I think.
Source V. Hartikainen
Abstract Ellipses Background Grayscale
Source GDJ
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
Sharp pixel pattern, just like the good old days.
Source Paridhi
Light gray grunge wall with a nice texture overlay.
Source Adam Anlauf
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
More in the paper realm, this time with fibers.
Source Jorge Fuentes