A seamless pattern formed from a modified version of rwwgub's tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
A dark metal plate with an embossed grid pattern and a bit of rust. Here's a dark metal plate texture for use as a tiled background on web pages.
Source V. Hartikainen
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
All good things come in threes, so I give you the third in my little concrete wall series.
Source Atle Mo
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin