Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
In the spirit of WWDC 2011, here is a dark iOS inspired linen pattern.
Source Atle Mo
Geometric lines are always hot, and this pattern is no exception.
Source Listvetra
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
The original enhanced with one of Inkscapes's filters.
Source Firkin
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
A car pattern?! Can it be subtle? I say yes!
Source Radosław Rzepecki
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
Remix from a drawing in 'Ostatnie chwile powstania styczniowego', Zygmunt Sulima, 1887.
Source Firkin
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A free seamless background image with a texture of dark red "canvas". It should look very nice on web sites.
Source V. Hartikainen