A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
I have no idea what J Boo means by this name, but hey – it’s hot.
Source j Boo
A black tile-able background with paper-like texture.
Source V. Hartikainen
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
From a drawing in 'A Life Interest', Mrs Alexander, 1888.
Source Firkin
Prismatic Hypnotic Pattern 2 No Background
Source GDJ
A seamless pattern with wide vertical stripes colored in pale yellow.
Source V. Hartikainen
A smooth mid-tone gray, or low contrast if you will, linen pattern.
Source Jordan Pittman
This is a remix of "blue wave-seigaiha".I hope this subtle color version of Seigaiha would be suitable for background .
Source Yamachem
Bigger is better, right? So here you have some large carbon fiber.
Source Factorio.us Collective
Prismatic Groovy Concentric Background No Black
Source GDJ
A dark background pattern/texture of a dimpled metal plate.
Source V. Hartikainen
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
A free seamless background with pink spots.
Source V. Hartikainen
An emulated “transparent” background pattern, like that of all kinds of computer graphics software.
Source AdamStanislav
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Fix side and a seamless pattern formed from circles.
Source SliverKnight