Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A seamless texture of a rough concrete surface.
Source V. Hartikainen
Prismatic Geometric Pattern Background No Black
Source GDJ
A bit strange this one, but nice at the same time.
Source Diogo Silva
You were craving more leather, so I whipped this up by scanning a leather jacket.
Source Atle Mo
This seamless light brown background texture resembles a wallpaper with vertical stripes. One way to use it is as a tiled background on web sites.
Source V. Hartikainen
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
Sounds French. Some 3D square diagonals, that’s all you need to know.
Source Graphiste
This ons is quite old school looking. Retro, even. I like it.
Source Arno Declercq
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Turn your site into a dragon with this great scale pattern.
Source Alex Parker
Remixed from a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
You can never get enough of these tiny pixel patterns with sharp lines.
Source Designova
Abstract Ellipses Background Grayscale
Source GDJ
From a drawing in 'Hyde Park from Domesday-Book to date', John Ashton, 1896.
Source Firkin
This background pattern looks like bamboo to me. Feel free to download it for your website (for your blog perhaps?).
Source V. Hartikainen
Black brick wall pattern. Brick your site up!
Source Alex Parker
As simple and subtle as it gets. But sometimes that’s just what you want.
Source Designova