To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Can never have too many knitting patterns, especially as nice as this.
Source Victoria Spahn
Vertical lines with a bumpy, yet crisp, feel to it.
Source Raasa
This is the remix of "Strawberry Pattern Background" uploaded by "GDJ". Thanks. I realigned strawberries so as to get seamless and changed the BG color.
Source Yamachem
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Sharp but soft triangles in light shades of gray.
Source Pixeden
A background pattern with a look of rough fabric.
Source V. Hartikainen
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
Luxurious looking pattern (for a T-shirt maybe?) with a hint of green.
Source Simon Meek
Prismatic Basic Pattern 2 No Background
Source GDJ
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
From a drawing of the coat of arms of the Ottoman Empire on Wikimedia.
Source Firkin
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Continuing the geometric trend, here is one more.
Source Mike Warner
Dead simple but beautiful horizontal line pattern.
Source Fabian Schultz
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso