From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Abstract Ellipses Background Grayscale
Source GDJ
A car pattern?! Can it be subtle? I say yes!
Source Radosław Rzepecki
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
Embossed lines and squares with subtle highlights.
Source Alex Parker
A repeating gloomy background image. This one consists of a pattern of black chains layered on top of a dark textured background.
Source V. Hartikainen
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
Zero CC tileable Laminate wood texture, photographed and made by me. CC0
Source Sojan Janso
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
A smooth mid-tone gray, or low contrast if you will, linen pattern.
Source Jordan Pittman
Prismatic Groovy Concentric Background
Source GDJ
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
Prismatic Polka Dots Mark II 3 No Background
Source GDJ
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
One more in the line of patterns inspired by Japanese/Asian styles. Smooth.
Source Kim Ruddock
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso