Prismatic Polka Dots Mark II 2 No Background
Source GDJ
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
Prismatic Hypnotic Pattern 2 No Background
Source GDJ
Not sure if this is related to the Nami you get in Google image search, but hey, it’s nice!
Source Dertig Media
Inspired by a pattern found in 'A General History of Hampshire, or the County of Southampton, including the Isle of Wight', Bernard Woodwood, 1861
Source Firkin
You may use it as is, or modify it as you like.
Source V. Hartikainen
A dark metal plate with an embossed grid pattern and a bit of rust. Here's a dark metal plate texture for use as a tiled background on web pages.
Source V. Hartikainen
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin