This light blue background pattern is quite pleasing to the eye, it consists of a tiny rough grid pattern, which is seamless by design. That's it, if you like the color, you can use this seamless pattern in a web design without making any further modifications to it.
Source V. Hartikainen
Everyone loves a diamond, right? Make your site sparkle.
Source AJ Troxell
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Dark pattern with some nice diagonal stitched lines crossing over.
Source Ashton
From a drawing in 'Friend or Fortune? The story of a strange year', Robert Overton, 1897.
Source Firkin
Prismatic Abstract Geometric Background 2
Source GDJ
Dark blue concrete wall with some small dust spots.
Source Atle Mo
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
A seamless background pattern with impressed gray dots.
Source V. Hartikainen
Tiny, tiny 3D cubes. Reminds me of the good old pattern from k10k.
Source Etienne Rallion
You can never get enough of these tiny pixel patterns with sharp lines.
Source Designova
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Not the Rebel alliance, but a dark textured pattern.
Source Hendrik Lammers
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
An alternative colour scheme to the original seamless pattern.
Source Firkin