As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
Prismatic Groovy Concentric Background No Black
Source GDJ
A dark metallic background with a pattern of stamped dots. Here's a dark "metallic" background pattern for you.
Source V. Hartikainen
Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Abstract Ellipses Background Grayscale
Source GDJ
The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
An abstract texture of black metal pipes (seamless).
Source V. Hartikainen
An aged paper background tile with smeared and pressed text.
Source V. Hartikainen
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Small dots with minor circles spread across to form a nice mosaic.
Source John Burks
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
Thin lines, noise and texture creates this crisp dark denim pattern.
Source Marco Slooten