A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
The image depicts a seamless pattern of pine tree leaves.
Source Yamachem
A seamless pattern formed from miutopia mug remixes on a tablecloth.
Source Firkin
After 1 comes 2, same but different. You get the idea.
Source Hendrik Lammers
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
Prismatic Basic Pattern 2 No Background
Source GDJ
A bit simplified version. Although it could be edited out to be simpler. Anyway, this time the tiling is converted to a pattern fill -which is using clipping for the tile's edges.
Source Lazur URH
This was formed by distorting an image of a background on Pixabay.
Source Firkin
A very dark asfalt pattern based off of a photo taken with my iPhone.
Source Atle Mo
From a drawing in 'Real Sailor-Songs', John Ashton, 1891.
Source Firkin