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
Colour version of the original pattern.
Source Firkin
Psychedelic Geometric Background No Black
Source GDJ
Seamless Olive Green Web Background Image
Source V. Hartikainen
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Remixed from a drawing in 'Analecta Eboracensia', Thomas Widdrington, 1897.
Source Firkin
This is a hot one. Small, sharp and unique.
Source GraphicsWall
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
From an image on opengameart.org shared by rubberduck.
Source Firkin
Run a restaurant blog? Here you go. Done.
Source Andrijana Jarnjak
From a drawing in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
A dark pattern made out of 3×3 circles and a 1px shadow. This works well as a carbon texture or background.
Source Atle Mo
Dark, square, clean and tidy. What more can you ask for?
Source Jaromír Kavan
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin