It’s big, it’s gradient—and it’s square.
Source Brankic1979
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Like the name suggests, this background image consists of a pattern of dark bricks. It may be an option for you, if you are looking for something that looks like a brick wall for use as a background on web pages. It's not a masterpiece, but looks pretty nice when is tiled.
Source V. Hartikainen
Inspired by a drawing seen in 'City of Liverpool', James Picton, 1883.
Source Firkin
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Lovely light gray floral motif with some subtle shades.
Source GraphicsWall
Prismatic Triangular Background Design Mark II 5
Source GDJ
Looks like an old wall. I guess that’s it then?
Source Viahorizon
Continuing the geometric trend, here is one more.
Source Mike Warner
Sharp pixel pattern, just like the good old days.
Source Paridhi
Same as the black version, but now in shades of gray. Very subtle and fine grained.
Source Atle Mo
Prismatic Triangular Background Design Mark II 5
Source GDJ
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin