The classic notebook paper with horizontal stripes.
Source Are Sundnes
Looks like an old wall. I guess that’s it then?
Source Viahorizon
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay
An emulated “transparent” background pattern, like that of all kinds of computer graphics software.
Source AdamStanislav
Actually, there's no clouds in it, but I think it looks quite nice.
Source V. Hartikainen
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
From a drawing in 'Uit de geschiedenis der Heilige Stede te Amsterdam', Yohannes Sterck, 1898.
Source Firkin
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Number 4 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.
Source Nathan Spady
Retro Circles Background 4 No Black
Source GDJ
Seamless Prismatic Quadrilateral Line Art Pattern No Background
Source GDJ
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
A seamless background texture of old cardboard.
Source V. Hartikainen
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
From a drawing in 'Cowdray: the history of a great English House', Julia Roundell, 1884.
Source Firkin
Has nothing to do with toast, but it’s nice and subtle.
Source Pippin Lee
A light gray wall or floor (you decide) of concrete.
Source Atle Mo