Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Tiny, tiny 3D cubes. Reminds me of the good old pattern from k10k.
Source Etienne Rallion
Remixed from a drawing in 'An Index to Deering's Nottinghamia Vetus et Nova', Rupert Chicken, 1899. The unit tile can be had by selecting the rectangle in Inkscape and using shift-alt-i
Source Firkin
You could get a bit dizzy from this one, but it might come in handy.
Source Dertig Media
Here's an yet another background for websites, with a seamless texture of wood planks this time.
Source V. Hartikainen
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
A frame using leaves from an image that was uploaded to Pixabay by mayapujiati
Source Firkin
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
This is the remix of "Tileable Wave Pattern 2" uploaded by "Arvin61r58".Thanks.I added a wire-mesh fence seamless pattern as a lower layer.
Source Yamachem
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Prismatic Hypnotic Pattern No Background
Source GDJ
A new one called white wall, not by me this time.
Source Yuji Honzawa
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
A very dark spotted twinkle pattern for your twinkle needs.
Source Badhon Ebrahim
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
Continuing the geometric trend, here is one more.
Source Mike Warner
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight