Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
The image depicts a shell seamless pattern.I used an OCAL clipart called "Shell" uploaded by "jgm104".Thanks.
Source Yamachem
A pattern drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A white version of the very popular linen pattern.
Source Ant Ekşiler
Prismatic Curved Diamond Pattern 2 No Background
Source GDJ
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Classy golf-pants pattern, or crossed stripes if you will.
Source Will Monson
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
A new one called white wall, not by me this time.
Source Yuji Honzawa
Simple combination of stripy squares with their negatively coloured counterparts
Source Firkin
Formed by heavily distorting part of a an image of a fish uploaded to Pixabay by GLady
Source Firkin
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
More in the paper realm, this time with fibers.
Source Jorge Fuentes
Abstract Ellipses Background Grayscale
Source GDJ
Submitted as a black pattern, I made it light and a few steps more subtle.
Source Andy
The perfect pattern for all your blogs about type, or type-related matters.
Source Atle Mo
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
From a drawing in 'Friend or Fortune? The story of a strange year', Robert Overton, 1897.
Source Firkin
This ons is quite old school looking. Retro, even. I like it.
Source Arno Declercq