A heavy dark gray base, some subtle noise and a 45-degree grid makes this look like a pattern with a tactile feel to it.
Source Atle Mo
A cute x, if you need that sort of thing.
Source Juan Scrocchi
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
This could be a hippy vintage wallpaper.
Source Tileable Patterns
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein