A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Prismatic Abstract Background Design No Black
Source GDJ
A bit like some carbon, or knitted netting if you will.
Source Anna Litvinuk
Very simple, very blu(e). Subtle and nice.
Source Seb Jachec
Looks like an old wall. I guess that’s it then?
Source Viahorizon
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
Classic vertical lines, in all its subtlety.
Source Cody L
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
"Beige Stone", Tileable Texture.
Source V. Hartikainen
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
Prismatic Curved Diamond Pattern 5 No Background
Source GDJ
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Nasty or not, it’s a nice pattern that tiles. Like they all do.
Source Badhon Ebrahim
Sharp pixel pattern looking like some sort of fabric.
Source Dmitry
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
The following repeating website background is colored in a blue gray color and resembles a concrete wall or something similar to it.
Source V. Hartikainen
This is a more minute version of "fishnet 01".The image depicts a seamless pattern of a fishnet with a plenty of fish.It may be a lucky charm for fishermen.
Source Yamachem