Here's a subtle marble-like background for use on websites.
Source V. Hartikainen
Remixed from a drawing that was uploaded to Pixabay by ractapopulous
Source Firkin
It’s an egg, in the form of a pattern. This really is 2012.
Source Paul Phönixweiß
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
Here's a tile-able wood background image for use in web design.
Source V. Hartikainen
White handmade paper pattern with small bumps.
Source Marquis
Sharp diamond pattern. A small 24x18px tile.
Source Tom Neal
Background formed from the iconic plastic construction bricks that gave me endless hours of fun when I was a lad.
Source Firkin
Sounds like something from World of Warcraft. Has to be good.
Source Tony Kinard
Not the most creative name, but it’s a good all-purpose light background.
Source Dmitry
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A seamless pattern formed from cross 4. To get the original tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Clean and crisp lines all over the place. Wrap it up with this one.
Source Dax Kieran
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Prismatic Curved Diamond Pattern 7 No Background
Source GDJ
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
The name is totally random, but hey, it sounds good.
Source Atle Mo
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin