To get the repeating unit, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
Zero CC tileable grass texture, photographed and made by me. CC0
Source Sojan Janso
A re-make of the Gradient Squares pattern.
Source Dimitar Karaytchev
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A comeback for you: the popular Escheresque, now in black.
Source Patten
Remixed from an image that was uploaded to Pixabay by KirstenStar
Source Firkin
One more sharp little tile for you. Subtle circles this time.
Source Blunia
A light brushed aluminum pattern for your pleasure.
Source Tim Ward
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
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
Abstract Tiled Background Extended 10
Source GDJ
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
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Seamless Dark Grunge Texture. Here's a new grunge texture for use as a background.
Source V. Hartikainen
Prismatic Polka Dots 3 No Background
Source GDJ
This one looks like a cork panel. Feel free to use it as a tiled background on your blog or website.
Source V. Hartikainen
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
Nice little grid. Would work great as a base on top of some other patterns.
Source Arno Gregorian