A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Colorful Floral Background 3 No Black
Source GDJ
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Classic vertical lines, in all its subtlety.
Source Cody L
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
From a drawing in 'Worsborough; its historical associations and rural attractions', Joseph Wilkinson, 1879.
Source Firkin
Embossed lines and squares with subtle highlights.
Source Alex Parker
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
Pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin
Some rectangles, a bit of dust and grunge, plus a hint of concrete.
Source Atle Mo
Prismatic Geometric Pattern Background
Source GDJ
A free background pattern with abstract green tiles.
Source V. Hartikainen
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
Simple combination of stripy squares with their negatively coloured counterparts
Source Firkin
Derived from an image that was uploaded to Pixabay by TheDigitalArtist
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Prismatic Abstract Background Design
Source GDJ
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso