Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
This ladies and gentlemen, is texturetastic! Love it.
Source Adam Pickering
Feel free to use this seamless background texture as a background on a web site. It's colored in a light pink color and is seamlessly tile-able.
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A lovely light gray pattern with stripes and a dash of noise.
Source V. Hartikainen
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Classy golf-pants pattern, or crossed stripes if you will.
Source Will Monson
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
One more brick pattern. A bit more depth to this one.
Source Benjamin Ward
Inspired by an image that was uploaded to Pixabay by geralt
Source Firkin
A bit like some carbon, or knitted netting if you will.
Source Anna Litvinuk
A free pink background pattern.
Source V. Hartikainen
The image depicts a seamless pattern which includes hexagonally-aligned gourds with BG in light-brown.
Source Yamachem
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow