A seamless background texture of old cardboard.
Source V. Hartikainen
With a name this awesome, how can I go wrong?
Source Nikolay Boltachev
Bigger is better, right? So here you have some large carbon fiber.
Source Factorio.us Collective
A seamless pale yellow paper background with a pattern of animal tracks.
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
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
Prismatic Snowflakes Pattern 3 No Background
Source GDJ
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Prismatic Groovy Concentric Background 5
Source GDJ
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
Sharp pixel pattern looking like some sort of fabric.
Source Dmitry
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
A seamless pattern made from the gold Penrose triangle by GDJ and the two remixes
Source Firkin
Prismatic Abstract Geometric Background 3
Source GDJ
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
It looks very nice I think.
Source V. Hartikainen
Background Wall, Art Abstract, Star Well & CC0 texture.
Source Ractapopulous
A nice looking light gray background pattern with diagonal stripes.
Source V. Hartikainen