Greek key pattern 5 #2294
 Dark  CC 0

Seamless pattern made from a tile that can be obtained in Inkscape by selecting the rectangle and using shift+alt+i.

Source Firkin

 More Textures
Carbon Fiber v2 #105
 Carbon  CC BY-SA 3.0

One more updated pattern. Not really carbon fiber, but it’s the most popular pattern, so I’ll give you an extra choice.

Source Atle Mo

Prismatic Curved Diamond Pattern 8 No Background #549
 Dark  CC 0

Prismatic Curved Diamond Pattern 8 No Background

Source GDJ

Robots #125
 Dark  CC BY-SA 3.0

And some more testing, this time with Seamless Studio. It’s Robots FFS!

Source Seamless Studio

Dark Brown Leather Texture, Seamless Tile #1092
 Leather  CC BY-SA 3.0

The texture of this background image has some similarities with leather, and it's colored in a dark brown color. So, if you are looking for a dark brown background image for your website, this may be an option for you.

Source V. Hartikainen

Background pattern 2 #221
 Noise  CC 0

A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.

Source Firkin

Gold Triangular Seamless Pattern No Background #272
 Light  CC 0

Gold Triangular Seamless Pattern No Background

Source GDJ

Green Dust & Scratches #107
 Wall  CC BY-SA 3.0

Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.

Source Atle Mo

Dark Wood #320
 Wood  CC BY-SA 3.0

A beautiful dark wood pattern, superbly tiled.

Source Omar Alvarado

Background pattern 272 (colour 3) #2055
 Red  CC 0

A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.

Source Firkin

Background pattern 306 (colour 2) #1881
 Colorful  CC 0

Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.

Source Firkin

Snowflake remix #155
 Dark  CC 0

A bit simplified version. Although it could be edited out to be simpler. Anyway, this time the tiling is converted to a pattern fill -which is using clipping for the tile's edges.

Source Lazur URH

Prismatic Rounded Squares Grid 4 No Background #491
 Noise  CC 0

Prismatic Rounded Squares Grid 4 No Background

Source GDJ

Light Honeycomb #59
 Light  CC BY-SA 3.0

Light honeycomb pattern made up of the classic hexagon shape.

Source Federica Pelzel

Background pattern 223 (colour 4) #2350
 Pink  CC 0

Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.

Source Firkin

White Plaster@2X #369
 Wall  CC BY-SA 3.0

Sweet and subtle white plaster with hints of noise and grunge.

Source Phil Maurer