Triangles #127
 Dark  CC BY-SA 3.0

Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.

Source Ivan Ginev

 More Textures
Prismatic Abstract Geometric Background 4 No Black #441
 Dark  CC 0

Prismatic Abstract Geometric Background 4 No Black

Source GDJ

Background pattern 215 (colour 4) #2368
 Green  CC 0

A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.

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

Decorative divider 253 #2064
 Dark  CC 0

From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.

Source Firkin

Dark Brick Wall #135
 Wall  CC BY-SA 3.0

Black brick wall pattern. Brick your site up!

Source Alex Parker

Wood Background Pattern #882
 Wood  CC BY-SA 3.0

A seamless background pattern with a texture of wood planks. This wood background pattern has vertically arranged planks. You may try to rotate it 90°, to see how it will look like when the wood planks are arranged horizontally.

Source V. Hartikainen