Here's a tile-able wood background image for use in web design.
Source V. Hartikainen
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
I love these crisp, tiny, super subtle patterns.
Source Badhon Ebrahim
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
This background pattern contains a seamless texture of bark. It's not very realistic, but I think it looks quite nice.
Source V. Hartikainen
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A white version of the very popular linen pattern.
Source Ant Ekşiler
The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
Can never have too many knitting patterns, especially as nice as this.
Source Victoria Spahn
To get the tile this is made up from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
A car pattern?! Can it be subtle? I say yes!
Source Radosław Rzepecki
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin
Used correctly, this could be nice. Used in a bad way, all hell will break loose.
Source Atle Mo