Actually remixed from a pattern on Pixabay. But then noticed a very similar one on Openclipart.org uploaded by btj51q2.
Source Firkin
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Paper pattern with small dust particles and 45-degree strokes.
Source Atle Mo
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
A seamless web texture of "green stone".
Source V. Hartikainen
A seamless pattern with green and yellow diagonal lines on top of a white dotted background.
Source V. Hartikainen
Seamless Dark Grunge Texture. Here's a new grunge texture for use as a background.
Source V. Hartikainen
Colour version of the original pattern.
Source Firkin
A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
A dark striped seamless pattern suitable for use as a background on websites.
Source V. Hartikainen
This white background pattern has a seamless grunge style texture. Here's a white grunge style background pattern. Use it as a tiled background image on web sites or for other purposes.
Source V. Hartikainen
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The name tells you it has curves. Oh yes, it does!
Source Peter Chon
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
To get the tile this is based on, 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
A yellow tiled background... Blurriness, bokeh effect and rectangles pattern in one mix.
Source V. Hartikainen
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Prismatic Curved Diamond Pattern 2 No Background
Source GDJ
A set of paper filters. The base texture is generated the same way, only the compositing mode is varied.
Source Lazur URH