The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
A nice and simple white rotated tile pattern.
Source Another One
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
A seamless pattern of leopard skin. It should look nice as a background element on web pages.
Source V. Hartikainen
A seamless stone-like background for blogs or any other type of websites.
Source V. Hartikainen
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
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
Original minus the background
Source Firkin
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Abstract Line Art Pattern Background 2
Source GDJ