A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
There are many carbon patterns, but this one is tiny.
Source Designova
To get the tile this is made up from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Redrawn based on a drawing in 'По Сѣверо-Западу Россіи' Konstantin Sluchevsky, 1897.
Source Firkin
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
A seamless texture of a rough concrete surface.
Source V. Hartikainen
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin