This one needs to be used in small areas; you can see it repeat.
Source Luca
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Used correctly, this could be nice. Used in a bad way, all hell will break loose.
Source Atle Mo
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
Seamless Olive Green Web Background Image
Source V. Hartikainen
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin