To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Greyscale version of a pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin
From a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Zero CC tileable hard cover red book, scanned and made by me. CC0
Source Sojan Janso
A pale yellow background pattern with vertical stripes. The stripes are partially faded. I think this background image turned out pretty well, especially those faded stripes.
Source V. Hartikainen
Prismatic Groovy Concentric Background
Source GDJ
Psychedelic Geometric Background No Black
Source GDJ
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
A free seamless background texture that looks like a brown stone wall.
Source V. Hartikainen
Prismatic Abstract Geometric Background 2
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
Prismatic Geometric Tessellation Pattern 2 No Background
Source GDJ
White circles connecting on a light gray background.
Source Mark Collins
Prismatic Curved Diamond Pattern No Background
Source GDJ
Paper pattern with small dust particles and 45-degree strokes.
Source Atle Mo
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.