A seamless pattern created from a square tile. To get the tile, select the pattern in Inkscape and use shift+alt+i.
Source Firkin
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
More in the paper realm, this time with fibers.
Source Jorge Fuentes
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
Derived from an image that was uploaded to Pixabay by TheDigitalArtist
Source Firkin
Prismatic Groovy Concentric Background 4
Source GDJ
Remixed from a drawing that was uploaded to Pixabay by ractapopulous
Source Firkin
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay
You know I’m a sucker for these. Well-crafted paper pattern.
Source Mihaela Hinayon
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
Number five from the same submitter, makes my job easy.
Source Dima Shiper
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
Zero CC tileable moss or lichen covered stone texture, edited from pixabay. CC0
Source Sojan Janso
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
There are many carbon patterns, but this one is tiny.
Source Designova
More bright luxury. This is a bit larger than fancy deboss, and with a bit more noise.
Source Viszt Péter