From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Derived from an image that was uploaded to Pixabay by starchim01
Source Firkin
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
More in the paper realm, this time with fibers.
Source Jorge Fuentes
Feel free to download and use it, or see the rest of the dark background patterns that I have made. Anyway, I hope you will find something that you like.
Source V. Hartikainen
You know you love wood patterns, so here’s one more.
Source Richard Tabor
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A free seamless background image with a texture of dark red "canvas". It should look very nice on web sites.
Source V. Hartikainen
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
Love the style on this one, very fresh. Diagonal diamond pattern. Get it?
Source INS
The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.
Source Nathan Spady
Prismatic Basic Pattern 2 No Background
Source GDJ
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Background Wall, Art Abstract, Watercolor Vintage style CC0 texture.
Source Ractapopulous
Prismatic Groovy Concentric Background 4
Source GDJ
In the spirit of WWDC 2011, here is a dark iOS inspired linen pattern.
Source Atle Mo
A seamless background tile of aged paper with shabby look.
Source V. Hartikainen
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
Fix side and a seamless pattern formed from circles.
Source SliverKnight