Classic 45-degree pattern, light version.
Source Luke McDonald
This was submitted in a beige color, hence the name. Now it’s a gray paper pattern.
Source Konstantin Ivanov
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
This one is amazing, truly original. Go use it!
Source Viahorizon
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
A free web background image with a seamless concrete-like texture and an Indian-red color.
Source V. Hartikainen
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
From a drawing in 'Bond Slaves. The story of a struggle.', Isabella Varley, 1893.
Source Firkin
Here is a new seamless wood texture for using as blog or website backgrounds.
Source V. Hartikainen
A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Might not be super subtle, but quite original in its form.
Source Alex Smith
It’s a hole, in a pattern. On your website. Dig it!
Source Josh Green
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin