You could get a bit dizzy from this one, but it might come in handy.
Source Dertig Media
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
A seamless background of warped stripes on paper.
Source V. Hartikainen
A seamless pattern with wide vertical stripes colored in pale yellow.
Source V. Hartikainen
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
Pattern produced in Paint.net using the Vibrato plug-in.
Source Firkin
Spice up your next school project with this icon background.
Source Swetha
This one has rusty dark brown texture.
Source V. Hartikainen
Oh yes, it happened! A pattern in full color.
Source Atle Mo
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo
A bit of scratched up grayness. Always good.
Source Dmitry
Prismatic Hypnotic Pattern No Background
Source GDJ
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
A white version of the very popular linen pattern.
Source Ant Ekşiler
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Abstract Tiled Background Extended 8
Source GDJ
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
Could be paper, could be a Polaroid frame – up to you!
Source Chaos
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett