CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Same as Silver Scales, but in black. Turn your site into a dragon with this great scale pattern.
Source Alex Parker
A dark gray, sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
The perfect pattern for all your blogs about type, or type-related matters.
Source Atle Mo
Just like your old suit, all striped and smooth.
Source Alex Berkowitz
Redrawn based on a drawing in 'По Сѣверо-Западу Россіи' Konstantin Sluchevsky, 1897.
Source Firkin
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Prismatic Geometric Pattern Background No Black
Source GDJ
An abstract web texture of a polished blue stone (or does it look more like ice).
Source V. Hartikainen
A free web background image with a seamless concrete-like texture and an Indian-red color.
Source V. Hartikainen
8 by 8 pixels, and just what the title says.
Source pixilated
Element of beach pattern with background.
Source Rones
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Prismatic Snowflakes Pattern 3 No Background
Source GDJ
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
Zero CC tileable hard cover cells book texture, 4k, scanned and made by me. CC0
Source Sojan Janso
Prismatic Groovy Concentric Background 2
Source GDJ