You can never get enough of these tiny pixel patterns with sharp lines.
Source Designova
Prismatic Abstract Geometric Background 5
Source GDJ
A colourful background drawn originally in paint.net and vectorised in Vector Magic.
Source Firkin
Might not be super subtle, but quite original in its form.
Source Alex Smith
Sort of like the back of a wooden board. Light, subtle, and stylish, just the way we like it!
Source Nikolalek
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Crossing lines with a subtle emboss effect on a dark background.
Source Stefan Aleksić
Number 3 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
Black And White Floral Pattern Background from PDP.
Source GDJ
Inspired by a design found in 'Konstantinápolyi emlékeim', Miklos Chriszto, 1893.
Source Firkin
Inspired by a 1930s wallpaper pattern I saw on TV.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Sharp but soft triangles in light shades of gray.
Source Pixeden
This background has abstract texture with some similarities to wood.
Source V. Hartikainen
Small dots with minor circles spread across to form a nice mosaic.
Source John Burks
A free seamless background with pink spots.
Source V. Hartikainen