Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
From a drawing in 'Hubert Montreuil, or the Huguenot and the Dragoon', Francisca Ouvry, 1873.
Source Firkin
A pale yellow background pattern with vertical stripes. The stripes are partially faded. I think this background image turned out pretty well, especially those faded stripes.
Source V. Hartikainen
Geometric triangles seem to be quite hot these days.
Source Pixeden
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
Prismatic Groovy Concentric Background 2
Source GDJ
Lovely pattern with some good-looking non-random noise lines.
Source Zucx
Pattern produced in Paint.net using the Vibrato plug-in.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Derived from an image that was uploaded to Pixabay by TheDigitalArtist
Source Firkin
This background pattern has futuristic look. So, maybe it could be used on websites or blogs dedicated to video games?!
Source V. Hartikainen
From an image on opengameart.org shared by rubberduck.
Source Firkin
Prismatic Snowflakes Pattern No Background
Source GDJ
This light blue background pattern is quite pleasing to the eye, it consists of a tiny rough grid pattern, which is seamless by design. That's it, if you like the color, you can use this seamless pattern in a web design without making any further modifications to it.
Source V. Hartikainen