Green Fibers #91
 Dark  CC BY-SA 3.0

The green fibers pattern will work very well in grayscale as well.

Source Matteo Di Capua

 More Textures
Brushed Alum@2X #68
 Light  CC BY-SA 3.0

A light brushed aluminum pattern for your pleasure.

Source Tim Ward

Booze pattern #1727
 Noise  CC 0

The tile this is based on was adapted from an image that was uploaded to Pixabay by frolicsomepl. It can be had in Inkscape by selecting the rectangle and using shift+alt+i

Source Firkin

Retro Squares Background@2X #415
 Noise  CC 0

Retro Squares Background

Source GDJ

Black Linen@2X #64
 Dark  CC BY-SA 3.0

In the spirit of WWDC 2011, here is a dark iOS inspired linen pattern.

Source Atle Mo

Glass block pattern #2477
 Brown  CC 0

Produced using the clouds, flames and glass blocks plug-ins in Paint.net and the resulting .PNG vectorised with Vector Magic.

Source Firkin

Prismatic Curved Diamond Pattern 6 No Background@2X #546
 Dark  CC 0

Prismatic Curved Diamond Pattern 6 No Background

Source GDJ

Prismatic Hypnotic Pattern No Background@2X #572
 Noise  CC 0

Prismatic Hypnotic Pattern No Background

Source GDJ

Cross Stripes #47
 Dark  CC BY-SA 3.0

Nice and simple crossed lines in dark gray tones.

Source Stefan Aleksić

Pattern cleanup 4 #157
 Noise  CC 0

An attempt for cleaning up the original image in a few steps.

Source Lazur URH

Background pattern 259 (colour 6) #2097
 Blue  CC 0

Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i

Source Firkin

Black Scales #191
 Dark  CC BY-SA 3.0

Same as Silver Scales, but in black. Turn your site into a dragon with this great scale pattern.

Source Alex Parker