Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
Turn your site into a dragon with this great scale pattern.
Source Alex Parker
A seamless background tile of aged paper with shabby look.
Source V. Hartikainen
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
Used correctly, this could be nice. Used in a bad way, all hell will break loose.
Source Atle Mo
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
Prismatic Rounded Squares Grid 4 No Background
Source GDJ
This one is amazing, truly original. Go use it!
Source Viahorizon