The image depicts polka dot seamless pattern.
Source Yamachem
Crossing lines with a subtle emboss effect on a dark background.
Source Stefan Aleksić
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
This is a hot one. Small, sharp and unique.
Source GraphicsWall
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Dark Tile-able Grunge Texture. I think this texture can be classified as grunge. It's free and seamless, as always.
Source V. Hartikainen
The image depicts a seamless pattern of a Japanese family crest called "chidori" in Japanese .A chidori in Japanese means a plover in English.
Source Yamachem
An abstract texture of water. It's not perfect, but will do. You may download if you like it.
Source V. Hartikainen
A seamless web texture with illustration of pale color stains on canvas.
Source V. Hartikainen
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
Lovely pattern with splattered vintage speckles.
Source David Pomfret
A repeating background with dark brown stone-like texture and abstract pattern that looks like tree trunks.
Source V. Hartikainen
From a drawing in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin
The original enhanced with one of Inkscapes's filters.
Source Firkin
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien