Used correctly, this could be nice. Used in a bad way, all hell will break loose.
Source Atle Mo
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
An abstract texture of black metal pipes (seamless).
Source V. Hartikainen
A free web background image with a seamless concrete-like texture and an Indian-red color.
Source V. Hartikainen
Vertical lines with a bumpy, yet crisp, feel to it.
Source Raasa
Prismatic Abstract Geometric Background 4
Source GDJ
Zero CC tileable brick texture, photographed and made by me. CC0
Source Sojan Janso
Remixed from a drawing that was uploaded to Pixabay by captenpub.
Source Firkin
This background pattern looks like bamboo to me. Feel free to download it for your website (for your blog perhaps?).
Source V. Hartikainen
Use shift+alt+i on the selected rectangle in Inkscape to get the tile this is based on
Source Firkin
Background formed from the original with an emboss effect
Source GDJ
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Derived from a drawing in 'Elfrica. An historical romance of the twelfth century', Charlotte Boger, 1885
Source Firkin
Prismatic Abstract Geometric Background 3
Source GDJ
Abstract Stars Geometric Pattern Prismatic No Background
Source GDJ
Tiny little fibers making a soft and sweet look.
Source Badhon Ebrahim
Abstract Tiled Background Extended 11
Source GDJ
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Non-seamless pattern drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
From a drawing in 'Uit de geschiedenis der Heilige Stede te Amsterdam', Yohannes Sterck, 1898.
Source Firkin
Used in small doses, this could be a nice subtle pattern. Used on a large surface, it’s dirty!
Source Paul Reulat
A seamless pattern formed from a square tile based on a jpg on Pixabay. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin