This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!
Source V. Hartikainen
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
A seamless pattern based on a tile that can be achieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Just like your old suit, all striped and smooth.
Source Alex Berkowitz
Formed by heavily distorting part of a an image of a fish uploaded to Pixabay by GLady
Source Firkin
A bit of scratched up grayness. Always good.
Source Dmitry
Sounds like something from World of Warcraft. Has to be good.
Source Tony Kinard
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Everyone needs some stardust. Sprinkle it on your next project.
Source Atle Mo
From a design in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Sometimes you just need the simplest thing.
Source Fabricio
From a drawing in 'Less Black than we're painted', James Payn, 1884.
Source Firkin
Nasty or not, it’s a nice pattern that tiles. Like they all do.
Source Badhon Ebrahim
Might not be super subtle, but quite original in its form.
Source Alex Smith
Inspired by a pattern I saw in a 19th century book. This seamless pattern was created from a square tile. To get the tile, select the pattern in Inkscape and use shift+alt+i.
Source Firkin
There are many carbon patterns, but this one is tiny.
Source Designova
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Dark pattern with some nice diagonal stitched lines crossing over.
Source Ashton