Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Remixed from a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
Green Web Background, Seamless tile.
Source V. Hartikainen
Submitted in a cream color, but you know how I like it.
Source Devin Holmes
Zero CC tileable yellow craft paper; scanned and made by me. CC0
Source Sojan Janso
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
This is so subtle: We’re talking 1% opacity. Get your squint on!
Source Atle Mo
A lovely light gray pattern with stripes and a dash of noise.
Source V. Hartikainen
Here's a subtle marble-like background for use on websites.
Source V. Hartikainen
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
A free tileable background colored in off-white (antique white) color.
Source V. Hartikainen
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
Another fairly simple design drawn in Paint.net and vectorized in Inkscape.
Source Firkin
Prismatic Hexagonalist Pattern No Background
Source GDJ
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
A seamless pattern formed from background pattern 102
Source Firkin
Looks like an old wall. I guess that’s it then?
Source Viahorizon
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
A bit like some carbon, or knitted netting if you will.
Source Anna Litvinuk
A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH