Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
White handmade paper pattern with small bumps.
Source Marquis
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Prismatic Groovy Concentric Background
Source GDJ
A free background image with a seamless texture of cardboard. This texture of cardboard looks quite realistic, especially when is actually tiled.
Source V. Hartikainen
Remixed from a raster on Pixabay, that was uploaded by ArtsyBee.
Source Firkin
This one needs to be used in small areas; you can see it repeat.
Source Luca
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A seamless texture of black leather. I think it will look best when used in headers, footers or sidebars.
Source V. Hartikainen
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
Sharp pixel pattern, just like the good old days.
Source Paridhi
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
Here's a seamless brown cork board background texture. Feel free to download or reshare if you like.
Source V. Hartikainen
Remixed from a JPG that was uploaded to Pixabay by susanlu4esm
Source Firkin
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
A comeback for you: the popular Escheresque, now in black.
Source Patten
Remixed from a drawing in 'A Child of the Age', Francis Adams, 1894.
Source Firkin
A bit strange this one, but nice at the same time.
Source Diogo Silva