CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ
A seamlessly tile-able grunge background image.
Source V. Hartikainen
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
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
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
We have some linen patterns here, but none that are stressed. Until now.
Source Jordan Pittman
Nasty or not, it’s a nice pattern that tiles. Like they all do.
Source Badhon Ebrahim
A pale orange background pattern with glossy groove stripes.
Source V. Hartikainen
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 seamless pattern of "sewn stripes" colored in light gray.
Source V. Hartikainen