The classic notebook paper with horizontal stripes.
Source Are Sundnes
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A free seamless background pattern for use on websites.
Source V. Hartikainen
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
Prismatic Abstract Background Design
Source GDJ
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
Prismatic Snowflakes Pattern No Background
Source GDJ
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
Derived from a drawing in 'The Murmur of the Shells', Samuel Cowen, 1879.
Source Firkin
Prismatic Snowflakes Pattern 3 No Background
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo
Here's a new paper-like background for free use on personal and commercial projects (this applies to all background patterns here).
Source V. Hartikainen
From a drawing in 'Uit de geschiedenis der Heilige Stede te Amsterdam', Yohannes Sterck, 1898.
Source Firkin
From a design in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
Lovely pattern with some good-looking non-random noise lines.
Source Zucx
Farmer could be some sort of fabric pattern, with a hint of green.
Source Fabian Schultz