This background pattern contains a seamless texture of bark. It's not very realistic, but I think it looks quite nice.
Source V. Hartikainen
From a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo
Hey, you never know when you’ll need a bird pattern, right?
Source Pete Fecteau
This was formed by distorting an image of a background on Pixabay.
Source Firkin
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.
Source Nathan Spady
This seamless pattern consists of a blue grid on a yellow background.
Source V. Hartikainen
Love the style on this one, very fresh. Diagonal diamond pattern. Get it?
Source INS
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Prismatic Geometric Tessellation Pattern No Background
Source GDJ
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
Number five from the same submitter, makes my job easy.
Source Dima Shiper
Abstract Tiled Background Extended 12
Source GDJ
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
Might not be super subtle, but quite original in its form.
Source Alex Smith
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
By popular request, an outline version of the pentagon pattern.
Source Atle Mo
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
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