The tile this fill pattern is based on can be had by using shift+alt+i on the rectangle.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
A comeback for you: the popular Escheresque, now in black.
Source Patten
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Number 3 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Geometric triangles seem to be quite hot these days.
Source Pixeden
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Zero CC tileable cork floor, photographed and made by me. CC0
Source Sojan Janso
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
Seamless Prismatic Quadrilateral Line Art Pattern No Background
Source GDJ
A lovely light gray pattern with stripes and a dash of noise.
Source V. Hartikainen
Some rectangles, a bit of dust and grunge, plus a hint of concrete.
Source Atle Mo
Zero CC tileable brick texture, photographed and made by me. CC0
Source Sojan Janso
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
This yellow background consists of a pattern of glossy gold buttons arranged in polka dot style on a seamless texture. Here's a pale yellow background pattern. Feel free to use it for your needs!
Source V. Hartikainen
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
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
Sometimes you just need the simplest thing.
Source Fabricio