Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
A seamless background pattern with impressed gray dots.
Source V. Hartikainen
Abstract Stars Geometric Pattern Prismatic No Background
Source GDJ
One more brick pattern. A bit more depth to this one.
Source Benjamin Ward
A seamless background tile of aged paper with shabby look.
Source V. Hartikainen
A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
Background formed from the original with an emboss effect
Source GDJ
A repeatable image with dark background and metal grid pattern.
Source V. Hartikainen
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
Black brick wall pattern. Brick your site up!
Source Alex Parker
From a drawing in 'Worsborough; its historical associations and rural attractions', Joseph Wilkinson, 1879.
Source Firkin
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
Prepared mostly as a raster in Paint.net and vectorised.
Source Firkin
The image is a remix of "edo pattern-samekomon".I changed the color of dots from black to white and added BG in light-yellow.
Source Yamachem
Honestly, who does not like a little pipe and mustache?
Source Luca Errico
Just what the name says, paper fibers. Always good to have.
Source Heliodor jalba
Prismatic Abstract Line Art Pattern Background
Source GDJ
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
A dark brown fabric-like background texture with seamless pattern of winding stripes.
Source V. Hartikainen
A colourful background drawn originally in paint.net and vectorised in Vector Magic.
Source Firkin
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
This was formed by distorting an image of a background on Pixabay.
Source Firkin