Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
There are many carbon patterns, but this one is tiny.
Source Designova
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Here's a brown background pattern with subtle stripes. I hope you'll like the color. If not, feel free to change it using an image editor, if you know how of course. Personally, I'm using GIMP to create these backgrounds.
Source V. Hartikainen
Inspired by a design found in 'Konstantinápolyi emlékeim', Miklos Chriszto, 1893.
Source Firkin
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Sounds like something from World of Warcraft. Has to be good.
Source Tony Kinard
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Geometric Pattern Background
Source GDJ
You know I’m a sucker for these. Well-crafted paper pattern.
Source Mihaela Hinayon
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
A heavy hitter at 400x400px, but lovely still.
Source Breezi
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
A repeating background with seamless texture of stone. There haven't been any stone-like backgrounds for a while, so I have decided to create one more. The rest can be found in the appropriate category.
Source V. Hartikainen
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
He influenced us all. “Don’t be sad because it’s over. Smile because it happened.”
Source Atle Mo
A repeating background of beige (or is it more vanilla yellow) textured stripes. One more background with stripes.
Source V. Hartikainen
Horizontal and vertical lines on a light gray background.
Source Adam Anlauf