Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
The Grid. A digital frontier. I tried to picture clusters of information as they traveled through the computer.
Source Haris Šumić
This seamless web background texture looks like gray stone. It's great for using as a background image on web pages, or on some of their elements. Anyway, I hope you will find use for it.
Source V. Hartikainen
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Prismatic Polka Dots Mark II No Background
Source GDJ
Same as Silver Scales, but in black. Turn your site into a dragon with this great scale pattern.
Source Alex Parker
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
This one is something special. I’d call it a flat pattern, too. Very well done, sir!
Source GetDiscount
More in the paper realm, this time with fibers.
Source Jorge Fuentes