Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Seamless Dark Grunge Texture. Here's a new grunge texture for use as a background.
Source V. Hartikainen
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
Did anyone say The Hoff? This pattern is in no way related to Baywatch.
Source Josh Green
It was called Navy Blue, but I made it dark. You know, the way I like it.
Source Ethan Hamilton
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
A dark striped seamless pattern suitable for use as a background on websites.
Source V. Hartikainen