Here's a bluish gray striped background pattern for use on web sites.
Source V. Hartikainen
Colour version of the original seamless pattern.
Source Firkin
From a drawing in 'Kingsdene', Maria Fetherstonehaugh, 1878.
Source Firkin
Subtle scratches on a light gray background.
Source Andrey Ovcharov
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
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
Almost like little fish shells, or dragon skin.
Source Graphiste
This one is amazing, truly original. Go use it!
Source Viahorizon
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
Zero CC bark from fur tree tileable texture, photographed and made by me. CC0
Source Sojan Janso
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin
Sort of reminds me of those old house wallpapers.
Source Tish
Looks like an old wall. I guess that’s it then?
Source Viahorizon
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
Prismatic Curved Diamond Pattern 7 No Background
Source GDJ
A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Otis Ray Redding was an American soul singer-songwriter, record producer, arranger, and talent scout. So you know.
Source Thomas Myrman
Background formed from the original with an emboss effect
Source GDJ