Sometimes you just need the simplest thing.
Source Fabricio
A seamless pattern of "sewn stripes" colored in light gray.
Source V. Hartikainen
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
A seamless pattern made from the gold Penrose triangle by GDJ and the two remixes
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Feel free to download this "Dark Wood" background texture for your web site. The background tiles seamlessly!
Source V. Hartikainen
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
A new one called white wall, not by me this time.
Source Yuji Honzawa
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
Actually, there's no clouds in it, but I think it looks quite nice.
Source V. Hartikainen
This could be a hippy vintage wallpaper.
Source Tileable Patterns
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
One more in the line of patterns inspired by Japanese/Asian styles. Smooth.
Source Kim Ruddock
f you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Black brick wall pattern. Brick your site up!
Source Alex Parker
A free grid paper background pattern for using on web sites.
Source V. Hartikainen
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
To get the tile this is made up from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Fix and cc0 to get the tile this is based on.
Source SliverKnight
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby