Inspired by this, I came up with this pattern. Madness!
Source Atle Mo
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
This is sort of fresh, but still feels a bit old school.
Source Martuchox
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
Colour version that is close to the original drawing uploaded to Pixabay by pencilparker.
Source Firkin
Derived from elements found in a floral ornament drawing on Pixabay.
Source Firkin
A lovely light gray pattern with stripes and a dash of noise.
Source V. Hartikainen
After 1 comes 2, same but different. You get the idea.
Source Hendrik Lammers
A free black metallic background pattern. Here's a new pattern I made that looks metallic.
Source V. Hartikainen
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Prismatic Curved Diamond Pattern 7 No Background
Source GDJ
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Background pattern made in "Grunge-Like" style. Available in both SVG and JPG formats. Edit to your needs then click the download button.
Source V. Hartikainen
Clover with background for St. Patrick's Day. Add to a card with a doily, ribbon, a leprechaun or other embellishments.
Source BAJ
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Seamless pattern formed from a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
A new take on the black linen pattern. Softer this time.
Source Atle Mo
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
Prismatic Groovy Concentric Background 2
Source GDJ
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin