A smooth mid-tone gray, or low contrast if you will, linen pattern.
Source Jordan Pittman
Use shift+alt+i on the selected rectangle in Inkscape to get the tile this is based on
Source Firkin
Seamless Prismatic Quadrilateral Line Art Pattern No Background
Source GDJ
Light gray paper pattern with small traces of fiber and some dust.
Source Atle Mo
In the spirit of WWDC 2011, here is a dark iOS inspired linen pattern.
Source Atle Mo
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
The following orange background pattern resembles a honeycomb.
Source V. Hartikainen
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin