Here's a subtle marble-like background for use on websites.
Source V. Hartikainen
Continuing the geometric trend, here is one more.
Source Mike Warner
Might not be super subtle, but quite original in its form.
Source Alex Smith
Pattern produced in Paint.net using the Vibrato plug-in.
Source Firkin
Crossing lines with a subtle emboss effect on a dark background.
Source Stefan Aleksić
Carbon fiber is never out of fashion, so here is one more style for you.
Source Alfred Lee
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Pattern Background, Texture, Photoshop Structure style CC0 texture.
Source Darkmoon1968
The image depicts a seamless pattern made using a bird's face.
Source Yamachem
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Zero CC tileable wood texture, made by me procedurally in Neo Texture Edit.
Source Sojan Janso
Remixed from a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
This light blue background pattern is quite pleasing to the eye, it consists of a tiny rough grid pattern, which is seamless by design. That's it, if you like the color, you can use this seamless pattern in a web design without making any further modifications to it.
Source V. Hartikainen
Stefan is hard at work, this time with a funky pattern of squares.
Source Stefan Aleksić
Retro Circles Background 5 No Black
Source GDJ
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks.
Pixel by pixel, sharp and clean. Very light pattern with clear lines.
Source M.Ashok