A set of paper filters. The base texture is generated the same way, only the compositing mode is varied.
Source Lazur URH
A free seamless background texture of "timber wall" (colored in dark brown).
Source V. Hartikainen
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
A seamless texture of a rough concrete surface.
Source V. Hartikainen
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The classic notebook paper with horizontal stripes.
Source Are Sundnes
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
Bright Multicolored Floral Background by Karen Arnold from PDP.
Source GDJ
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
That’s what it is, a dark dot. Or sort of carbon looking.
Source Tsvetelin Nikolov
Retro Circles Background 5 No Black
Source GDJ
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Prismatic Abstract Line Art Pattern Background
Source GDJ
A beautiful dark padded pattern, like an old classic sofa.
Source Chris Baldie
On a large canvas you can see it tiling, but used on smaller areas, it’s beautiful.
Source Paul Phönixweiß
A simple but elegant classic. Every collection needs one of these.
Source Christopher Burton
Formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
More tactile goodness. This time in the form of some rough cloth.
Source Bartosz Kaszubowski