A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
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
Prismatic Groovy Concentric Background No Black
Source GDJ
A pattern drawn in Paint.net and vectorized in Inkscape.
Source Firkin
Embossed lines and squares with subtle highlights.
Source Alex Parker
This seamless pattern consists of a blue grid on a yellow background.
Source V. Hartikainen
Turn your site into a dragon with this great scale pattern.
Source Alex Parker
A free background image with a seamless texture of cardboard. This texture of cardboard looks quite realistic, especially when is actually tiled.
Source V. Hartikainen
Vertical lines with a bumpy, yet crisp, feel to it.
Source Raasa
Remix from a drawing in 'Ostatnie chwile powstania styczniowego', Zygmunt Sulima, 1887.
Source Firkin
Used in small doses, this could be a nice subtle pattern. Used on a large surface, it’s dirty!
Source Paul Reulat
Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
A nice and simple white rotated tile pattern.
Source Another One
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Love me some light mesh on a Monday. Sharp.
Source Wilmotte Bastien
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo