A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
Prismatic Curved Diamond Pattern 5 No Background
Source GDJ
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A seamless pattern formed from background pattern 102
Source Firkin
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
Sharp diamond pattern. A small 24x18px tile.
Source Tom Neal
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A light background pattern with diagonal stripes. Here's a simple light striped background for you.
Source V. Hartikainen
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
A dark gray, sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
Black & white version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin