Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
A free grid paper background pattern for using on web sites.
Source V. Hartikainen
Embossed lines and squares with subtle highlights.
Source Alex Parker
White fabric looking texture with some nice random wave features.
Source Hendrik Lammers
Light gray grunge wall with a nice texture overlay.
Source Adam Anlauf
Kaleidoscope Prismatic Abstract No Background
Source GDJ
Remixed from a drawing in 'Line and form", Walter Crane, 1914.
Source Firkin
Zero CC plastic pattern texture, photographed and made by me. CC0 *Note, this texture was on the perfectly smooth surface of a plastic shovel scraper, not sure how to call it. Plz coment if you know what its called.
Source Sojan Janso
Remixed from a drawing in 'Hungary. A guide book. By several authors', 1890.
Source Firkin
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
Basket Fibers, Basket Texture, Braid Background style CC0 texture.
Source 1A-Photoshop
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a raster on Pixabay that was uploaded by ArtsyBee.
Source Firkin
Sweet and subtle white plaster with hints of noise and grunge.
Source Phil Maurer
A white version of the very popular linen pattern.
Source Ant Ekşiler
A repeatable image with dark background and metal grid pattern.
Source V. Hartikainen
Might not be super subtle, but quite original in its form.
Source Alex Smith
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Light and tiny, just the way you like it.
Source Rohit Arun Rao
One more brick pattern. A bit more depth to this one.
Source Benjamin Ward
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso