This was formed by distorting an image of a background on Pixabay.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A nice looking light gray background pattern with diagonal stripes.
Source V. Hartikainen
These dots are already worn for you, so you don’t have to.
Source Matt McDaniel
White handmade paper pattern with small bumps.
Source Marquis
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
Prismatic Polka Dots Mark II 3 No Background
Source GDJ
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
It’s okay to be square! A nice light gray pattern with random squares.
Source Waseem Dahman
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Produced using the clouds, flames and glass blocks plug-ins in Paint.net and the resulting .PNG vectorised with Vector Magic.
Source Firkin
Like the name suggests, this background image consists of a pattern of dark bricks. It may be an option for you, if you are looking for something that looks like a brick wall for use as a background on web pages. It's not a masterpiece, but looks pretty nice when is tiled.
Source V. Hartikainen
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
An interesting dark spotted pattern at an angle.
Source Hendrik Lammers
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Light and tiny, just the way you like it.
Source Rohit Arun Rao
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
Washi (和紙?) is a type of paper made in Japan. Here’s the pattern for you!
Source Carolynne
From a drawing in 'Az Osztrák-Magyar Monarchia irásban és képben', 1885.
Source Firkin
One more sharp little tile for you. Subtle circles this time.
Source Blunia
Inspired by a pattern found in 'A General History of Hampshire, or the County of Southampton, including the Isle of Wight', Bernard Woodwood, 1861
Source Firkin
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin