Soft Kill@2X #319
 Dark  CC BY-SA 3.0

Pattern #100! A black classic knit-looking pattern.

Source Factorio.us Collective

 More Textures
Interlocking pattern 3 #2406
 Grid  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

Dark Mosaic@2X #122
 Dark  CC BY-SA 3.0

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

Source John Burks

Lined Paper@2X #363
 Stripes  CC BY-SA 3.0

The classic notebook paper with horizontal stripes.

Source Are Sundnes

Tessellation 16 (colour 6) #2210
 Colorful  CC 0

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

Source Firkin

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

"Dark Brick Wall", Background Pattern #1024
 Stone  CC BY-SA 3.0

Like the name suggests, this background image consists of a pattern of dark bricks. It may be an option for you, if you are looking for something that looks like a brick wall for use as a background on web pages. It's not a masterpiece, but looks pretty nice when is tiled.

Source V. Hartikainen

Dark Stripes@2X #40
 Dark  CC BY-SA 3.0

Very dark pattern with some noise and 45-degree lines.

Source Stefan Aleksić

Decorative divider 229 #2151
 Dark  CC 0

From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.

Source Firkin

Psychedelic Geometric Background No Black #382
 Noise  CC 0

Psychedelic Geometric Background No Black

Source GDJ

Background pattern 215 (colour 2) #2370
 Blue  CC 0

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

Source Firkin

Background pattern 5 #224
 Noise  CC 0

A pattern drawn in Paint.net and vectorized in Inkscape.

Source Firkin

My Little Plaid #332
 Light  CC BY-SA 3.0

Repeating squares overlapping.

Source Pete Fecteau

Background pattern green #1950
 Green  CC 0

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

Source Firkin