Checkered Light Emboss #280
 Grid  CC BY-SA 3.0

Sort of like the Photoshop transparent background, but better!

Source Alex Parker

 More Textures
Retro Circles Background 7 No Black #433
 Unknow  CC 0

Retro Circles Background 7 No Black

Source GDJ

Prismatic Geometric Tessellation Pattern 2 No Background #553
 Noise  CC 0

Prismatic Geometric Tessellation Pattern 2 No Background

Source GDJ

Patern dots #241
 Dark  CC 0

Pattern repeating background 48x48

Source Keistutis

Diamond pattern (colour 4) #2282
 Blue  CC 0

From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.

Source Firkin

Gun Metal@2X #361
 Dark  CC BY-SA 3.0

With a name this awesome, how can I go wrong?

Source Nikolay Boltachev

Background pattern 8 (greyscale) #210
 Dark  CC 0

Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net

Source Firkin

Background pattern 248 (colour) #2180
 Yellow  CC 0

To get the tile this is made up from select the rectangle in Inkscape and use shift+alt+i.

Source Firkin

Black Mamba #57
 Dark  CC BY-SA 3.0

The name alone is awesome, but so is this sweet dark pattern.

Source Federica Pelzel

Electric recharge #163
 Noise  CC 0

Simple turbulence filter rigged in in inkscape.

Source Lazur URH

Background pattern purple #1946
 Colorful  CC 0

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

Source Firkin

Psychedelic Geometric Background #381
 Noise  CC 0

Psychedelic Geometric Background.

Source GDJ

Retro Circles Background 5@2X #425
 Noise  CC 0

Retro Circles Background 5

Source GDJ