Black Mamba #57
 Dark  CC BY-SA 3.0

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

Source Federica Pelzel

 More Textures
Inflicted #117
 Grid  CC BY-SA 3.0

Dark squares with some virus-looking dots in the grid.

Source Hugo Loning

Triangles pattern #2408
 Brown  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

Retro Squares Background 2@2X #417
 Noise  CC 0

Retro Squares Background 2

Source GDJ

Prismatic Abstract Line Art Pattern Background #565
 Dark  CC 0

Prismatic Abstract Line Art Pattern Background

Source GDJ

Diamond pattern (colour 7) #2274
 Red  CC 0

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

Source Firkin

Smooth Wall #27
 Light  CC BY-SA 3.0

Some rectangles, a bit of dust and grunge, plus a hint of concrete.

Source Atle Mo

Background pattern 252 (colour 6) #2157
 Light  CC 0

Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.

Source Firkin

Prismatic Polka Dots 3 No Background #528
 Noise  CC 0

Prismatic Polka Dots 3 No Background

Source GDJ

60º lines #25
 Light  CC BY-SA 3.0

Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.

Source Atle Mo

Prismatic Groovy Concentric Background 2 No Black #455
 Noise  CC 0

Prismatic Groovy Concentric Background 2 No Black

Source GDJ