From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
Prismatic Geometric Pattern Background
Source GDJ
From a drawing in 'Studies for Stories', Jean Ingelow, 1864.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Number 3 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
One more brick pattern. A bit more depth to this one.
Source Benjamin Ward
This pattern comes in orange, and it looks as if it is "made of glass".
Source V. Hartikainen
ZeroCC tileable beechwood wood texture, generated in Neo Texture Edit by me. CC0
Source Sojan Janso
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Geometric Pattern Background 2
Source GDJ
Remixed from a JPG that was uploaded to Pixabay by Osckar
Source Firkin
Remixed from a raster on Pixabay, that was uploaded by ArtsyBee.
Source Firkin
Drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
Psychedelic Geometric Background No Black
Source GDJ
A light background pattern with diagonal stripes. Here's a simple light striped background for you.
Source V. Hartikainen
A seamlessly tileable pink background texture.
Source V. Hartikainen
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin