More Textures
Dark Blue Gray Wallpaper Texture #901
 Stripes  CC BY-SA 3.0

This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!

Source V. Hartikainen

Robots #125
 Dark  CC BY-SA 3.0

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

Source Seamless Studio

Patern dots #241
 Dark  CC 0

Pattern repeating background 48x48

Source Keistutis

Background pattern 290 #1932
 Dark  CC 0

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

Source Firkin

Sports car pattern 2 #2441
 Colorful  CC 0

A seamless pattern formed from a sports car on clker.com. To get the tile, select the rectangle in Inkscape and use shift+alt+i.

Source Firkin

Prismatic Abstract Geometric Background 4 No Black@2X #443
 Dark  CC 0

Prismatic Abstract Geometric Background 4

Source GDJ

Noise Pattern With Subtle Cross Lines@2X #180
 Grid  CC BY-SA 3.0

More bright luxury. This is a bit larger than fancy deboss, and with a bit more noise.

Source Viszt Péter

Background pattern 339 (colour) #1708
 Yellow  CC 0

The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i

Source Firkin

Spiral pattern 3 #1934
 Dark  CC 0

From a drawing in 'Danmarks Riges Historie af J. Steenstrup, Kr. Erslev, A. Heise, V. Mollerup, J. A. Fridericia, E. Holm, A. D. Jørgensen', 1897.

Source Firkin

Dark Denim #29
 Dark  CC BY-SA 3.0

A dark denim looking pattern. 145×145 pixels.

Source Atle Mo

Background pattern 3 #222
 Noise  CC 0

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

Source Firkin

Zig-zag pattern 4 #2415
 Grid  CC 0

A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.

Source Firkin

Inflicted #117
 Grid  CC BY-SA 3.0

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

Source Hugo Loning