This was formed by distorting an image of a background on Pixabay.
Source Firkin
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.
Source Firkin
I skipped number 3, because it wasn’t all that great. Sorry.
Source Dima Shiper
It’s an egg, in the form of a pattern. This really is 2012.
Source Paul Phönixweiß
Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
Tiny circle waves, almost like the ocean.
Source Sagive
Used the 6th circle pattern designed by Viscious-Speed to create a print that can be used for card making or scrapbooking. Save as a PDF file for the best printing option.
Source Lovinglf
This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby
Inspired by a 1930s wallpaper pattern I saw on TV.
Source Firkin
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ
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
Inspired by a pattern I saw in a 19th century book. This seamless pattern was created from a square tile. To get the tile, select the pattern in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
You may use it as is, or modify it as you like.
Source V. Hartikainen
From a drawing in 'Friend or Fortune? The story of a strange year', Robert Overton, 1897.
Source Firkin
As the original image 's page size is too large for its image size, I remixed it.
Source Yamachem
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
A white version of the very popular linen pattern.
Source Ant Ekşiler