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
Dark Denim #372
 Dark  CC BY-SA 3.0

Thin lines, noise and texture creates this crisp dark denim pattern.

Source Marco Slooten

Background Patterns - Slate #244
 Fabric  CC 0

If you want png files of thisu can download them here :

Source Viscious-Speed

Colorful Floral Background 2 #487
 Dark  CC 0

Colorful Floral Background 2

Source GDJ

Light Aluminum #304
 Wall  CC BY-SA 3.0

Used correctly, this could be nice. Used in a bad way, all hell will break loose.

Source Atle Mo

Background pattern 238 #2229
 Red  CC 0

To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.

Source Firkin

Background pattern 117 #524
 Noise  CC 0

A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.

Source Firkin

Prismatic Geometric Tessellation Pattern 3 No Background@2X #556
 Noise  CC 0

Prismatic Geometric Tessellation Pattern 3 No Background

Source GDJ

Background pattern 333 #1741
 Noise  CC 0

The tile this is formed from can be retrieved in Inkscape by selecting the rectangle and using shift+alt+i

Source Firkin

Vintage pattern #2296
 Brown  CC 0

Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.

Source Firkin

Connected@2X #349
 Light  CC BY-SA 3.0

White circles connecting on a light gray background.

Source Mark Collins

Colourful bricks pattern (no background) #265
 Noise  CC 0

Original minus the background

Source Firkin

Dark Mosaic #121
 Dark  CC BY-SA 3.0

Small dots with minor circles spread across to form a nice mosaic.

Source John Burks

Background pattern 213 #2412
 Dark  CC 0

A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-i.

Source Firkin