Dark, lines, noise, tactile. You get the drift.
Source Anatoli Nicolae
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
Submitted by DomainsInfo – wtf, right? But hey, a free pattern.
Source DomainsInfo
Same as the black version, but now in shades of gray. Very subtle and fine grained.
Source Atle Mo
Abstract Tiled Background Extended 8
Source GDJ
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
With a name this awesome, how can I go wrong?
Source Nikolay Boltachev
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Remixed from an image that was uploaded to Pixabay by KirstenStar
Source Firkin
A seamless pale yellow paper background with a pattern of animal tracks.
Source V. Hartikainen
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
Alternative colour scheme to the original.
Source Firkin
This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!
Source V. Hartikainen
This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
Prismatic Curved Diamond Pattern 6 No Background
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin