From a drawing of the coat of arms of the Ottoman Empire on Wikimedia.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
You can never get enough of these tiny pixel patterns with sharp lines.
Source Designova
Used correctly, this could be nice. Used in a bad way, all hell will break loose.
Source Atle Mo
Here's a bluish gray striped background pattern for use on web sites.
Source V. Hartikainen
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
A version without colours blended together to give a different look.
Source Firkin
Lovely light gray floral motif with some subtle shades.
Source GraphicsWall
A nice looking light gray background pattern with diagonal stripes.
Source V. Hartikainen
I have no idea how to describe this one, but it’s light and delicate.
Source JBasoo
A light brushed aluminum pattern for your pleasure.
Source Tim Ward
Prismatic Groovy Concentric Background 3
Source GDJ
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
Sort of like the back of a wooden board. Light, subtle, and stylish, just the way we like it!
Source Nikolalek
A seamless pattern formed from a tile made from page ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Classy golf-pants pattern, or crossed stripes if you will.
Source Will Monson
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
Zero CC tileable bark texture, photographed and made by me. CC0
Source Sojan Janso
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso