CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Retro Circles Background 5 No Black
Source GDJ
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Three shades of gray makes this pattern look like a small carbon fiber surface. Great readability even for small fonts.
Source Atle Mo
A bit like some carbon, or knitted netting if you will.
Source Anna Litvinuk
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
White fabric looking texture with some nice random wave features.
Source Hendrik Lammers
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Prismatic Curved Diamond Pattern 2 No Background
Source GDJ
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Zero CC tileable bark texture, photographed and made by me. CC0
Source Sojan Janso
Sharp pixel pattern, just like the good old days.
Source Paridhi
The image depicts a pattern of regular hexagon.As I made to use it for myself,I want to others to use it.Speaking about the ratio of the image, height : width = 2 : √3(1.732...)Ridiculous to say,I realized later that this image is not honey comb pattern.I have to slide the second row.
Source Yamachem