As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
This ons is quite old school looking. Retro, even. I like it.
Source Arno Declercq
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A bit simplified version. Although it could be edited out to be simpler. Anyway, this time the tiling is converted to a pattern fill -which is using clipping for the tile's edges.
Source Lazur URH
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Derived from elements found in a floral ornament drawing on Pixabay.
Source Firkin
A comeback for you: the popular Escheresque, now in black.
Source Patten
Prismatic Groovy Concentric Background
Source GDJ
A seamless background tile of aged paper with shabby look.
Source V. Hartikainen
Black And White Floral Pattern Background Inverse
Source GDJ
A comeback for you: the popular Escheresque, now in black.
Source Patten
The act or state of corrugating or of being corrugated, a wrinkle; fold; furrow; ridge.
Source Anna Litvinuk
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Remixed from a vector adapted from a jpg on Pixabay. The tile this is constructed from can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin