The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Geometric lines are always hot, and this pattern is no exception.
Source Listvetra
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Turn your site into a dragon with this great scale pattern.
Source Alex Parker
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
An abstract pale yellow paper-like background with stains colored in yellow and green.
Source V. Hartikainen
A new take on the black linen pattern. Softer this time.
Source Atle Mo
From a drawing in 'Less Black than we're painted', James Payn, 1884.
Source Firkin
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
A black tile-able background with paper-like texture.
Source V. Hartikainen
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
Sounds like something from World of Warcraft. Has to be good.
Source Tony Kinard
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
Kaleidoscope Prismatic Abstract No Background
Source GDJ
Tile-able Dark Brown Wood Background. Feel free to use it as a background image in your designs or somewhere on the web. By the way, the color seems to be close to Coffee Brown.
Source V. Hartikainen
The following repeating website background is colored in a blue gray color and resembles a concrete wall or something similar to it.
Source V. Hartikainen
From a drawing in 'Picturesque New Guinea', J Lindt, 1887.
Source Firkin
Classic vertical lines, in all its subtlety.
Source Cody L
From a drawing in 'An Old Maid's Love. A Dutch tale told in English', Maarten Maartens, 1891.
Source Firkin
Seamless tile drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
A blue gray fabric-like texture for websites. An yet another fabric-like texture. It has subtle vertical and diagonal stripes to it.
Source V. Hartikainen