People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
This is so subtle: We’re talking 1% opacity. Get your squint on!
Source Atle Mo
Derived from an image that was uploaded to Pixabay by darkmoon1968
Source Firkin
A seamless pattern made from the gold Penrose triangle by GDJ and the two remixes
Source Firkin
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
Prismatic Abstract Line Art Pattern Background 2
Source GDJ
This makes me wanna shoot some pool! Sweet green pool table pattern.
Source Caveman
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A set of paper filters. The base texture is generated the same way, only the compositing mode is varied.
Source Lazur URH
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
Colour version of the original pattern inspired by the front cover of 'Old and New Paris', Henry Edwards, 1894.
Source Firkin
Carbon fiber is never out of fashion, so here is one more style for you.
Source Alfred Lee
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
Prismatic Curved Diamond Pattern 2 No Background
Source GDJ
A simple but elegant classic. Every collection needs one of these.
Source Christopher Burton
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin
A free seamless background image with a texture of dark red "canvas". It should look very nice on web sites.
Source V. Hartikainen
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
Inspired by an image that was uploaded to Pixabay by geralt
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
Fake or not, it’s quite luxurious.
Source Factorio.us Collective
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin