People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
An abstract Background pattern of purple twisty patterns.
Source TikiGiki
This is a remix of "blue wave-seigaiha".I hope this subtle color version of Seigaiha would be suitable for background .
Source Yamachem
Vector version of a JPG that was uploaded to Pixabay by theasad121
Source Firkin
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
First pattern tailor-made for Retina, with many more to come. All the old ones are upscaled, in case you want to re-download.
Source Atle Mo
I love these crisp, tiny, super subtle patterns.
Source Badhon Ebrahim
Classy golf-pants pattern, or crossed stripes if you will.
Source Will Monson
A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
A blue background wallpaper for websites. It has a seamless texture with vertical stripes. It looks quite nice not only when using as a tiled background on websites, but also on computer desktops.
Source V. Hartikainen
It’s okay to be square! A nice light gray pattern with random squares.
Source Waseem Dahman
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
That’s what it is, a dark dot. Or sort of carbon looking.
Source Tsvetelin Nikolov
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Lovely pattern with splattered vintage speckles.
Source David Pomfret
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Super dark, crisp and detailed. And a Kill Bill reference.
Source Badhon Ebrahim
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868.
Source Firkin