Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
Prismatic Geometric Pattern Background 2
Source GDJ
To celebrate the new feature, we need some sparkling diamonds.
Source Atle Mo
Prismatic Polka Dots 3 No Background
Source GDJ
Continuing the geometric trend, here is one more.
Source Mike Warner
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
Tile-able Dark Brown Wood Background. Feel free to use it as a background image in your designs or somewhere on the web. By the way, the color seems to be close to Coffee Brown.
Source V. Hartikainen
Tiny little fibers making a soft and sweet look.
Source Badhon Ebrahim
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
New paper pattern with a slightly organic feel to it, using some thin threads.
Source Atle Mo
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Sharp but soft triangles in light shades of gray.
Source Pixeden
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
Prismatic Geometric Pattern Background No Black
Source GDJ
Derived from a PNG that was uploaded to Pixabay by nutkitten
Source Firkin