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
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The tile can be had by using shift+alt+i on the selected rectangle in Inkscape
Source Firkin
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
Your eyes can trip a bit from looking at this – use it wisely.
Source Michal Chovanec
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
Prismatic Geometric Tessellation Pattern 2 No Background
Source GDJ
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Vertical lines with a bumpy, yet crisp, feel to it.
Source Raasa
Sharp pixel pattern, just like the good old days.
Source Paridhi
This was formed by distorting an image of a background on Pixabay.
Source Firkin
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
A seamless background pattern with impressed gray dots.
Source V. Hartikainen
Prismatic Abstract Background Design
Source GDJ
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Tiny little fibers making a soft and sweet look.
Source Badhon Ebrahim
Same as the black version, but now in shades of gray. Very subtle and fine grained.
Source Atle Mo
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
ZeroCC tileable moss texture, photographed and made by me. CC0
Source Sojan Janso
An attempt for cleaning up the original image in a few steps.
Source Lazur URH
A brown metallic grid pattern layered on top of a dark fabric texture. It should look great when using as a tiled background on web pages, especially blogs.
Source V. Hartikainen
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin