As simple and subtle as it gets. But sometimes that’s just what you want.
Source Designova
A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Prismatic Hexagonalist Pattern No Background
Source GDJ
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
You can never get enough of these tiny pixel patterns with sharp lines.
Source Designova
Remixed from an image on Pixabay, the original having been uploaded by darkmoon1968.
Source Firkin
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
A seamless background pattern with a texture of wood planks. This wood background pattern has vertically arranged planks. You may try to rotate it 90°, to see how it will look like when the wood planks are arranged horizontally.
Source V. Hartikainen
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
A seamless marble-like texture colored in light blue.
Source V. Hartikainen
Submitted in a cream color, but you know how I like it.
Source Devin Holmes
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
A seamless stone-like background for blogs or any other type of websites.
Source V. Hartikainen
Love me some light mesh on a Monday. Sharp.
Source Wilmotte Bastien
A background pattern with a look of rough fabric.
Source V. Hartikainen
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
A pattern formed from repeated instances of corner decoration 8. To get the basic tile select the rectangle in Inkscape and use shift+alt+i
Source Firkin