A heavy hitter at 400x400px, but lovely still.
Source Breezi
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Derived from elements found in a floral ornament drawing on Pixabay.
Source Firkin
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel
Colour version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
A light gray background pattern with seamless fabric-like texture and almost unnoticeable stripes.
Source V. Hartikainen
Abstract Ellipses Background Grayscale
Source GDJ
Prismatic Basic Pattern 2 No Background
Source GDJ
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
Remixed from a PNG that was uploaded to Pixabay by k_jprather
Source Firkin
A light gray fabric pattern with faded vertical stripes.
Source V. Hartikainen
8 by 8 pixels, and just what the title says.
Source pixilated
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin