A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Actually, there's no clouds in it, but I think it looks quite nice.
Source V. Hartikainen
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
Prismatic Geometric Pattern Background No Black
Source GDJ
Formed by heavily distorting part of a an image of a fish uploaded to Pixabay by GLady
Source Firkin
Psychedelic Geometric Background No Black
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Luxury pattern, looking like it came right out of Paris.
Source Daniel Beaton
Prismatic Geometric Pattern Background 2
Source GDJ
Pixel by pixel, sharp and clean. Very light pattern with clear lines.
Source M.Ashok
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
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
Some rectangles, a bit of dust and grunge, plus a hint of concrete.
Source Atle Mo
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
From a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Geometric triangles seem to be quite hot these days.
Source Pixeden
Prismatic Groovy Concentric Background No Black
Source GDJ
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo