Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Prismatic Geometric Pattern Background 2
Source GDJ
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
From a drawing in 'Danmarks Riges Historie af J. Steenstrup, Kr. Erslev, A. Heise, V. Mollerup, J. A. Fridericia, E. Holm, A. D. Jørgensen', 1897.
Source Firkin
The name is totally random, but hey, it sounds good.
Source Atle Mo
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
One more sharp little tile for you. Subtle circles this time.
Source Blunia
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
To get the repeating unit, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Spice up your next school project with this icon background.
Source Swetha
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
This was formed by distorting an image of a background on Pixabay.
Source Firkin
White circles connecting on a light gray background.
Source Mark Collins
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ