A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Neat little photography icon pattern.
Source Hossam Elbialy
From drawing in 'Musings in Maoriland', Thomas Bracken, 1890.
Source Firkin
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Hexagonal dark 3D pattern. What more can you ask for?
Source Norbert Levajsics
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This tiled background comes in red and consists of tiles that look like gemstones. It is more for blogs or social profiles, I think.
Source V. Hartikainen
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ
It’s a hole, in a pattern. On your website. Dig it!
Source Josh Green
After 1 comes 2, same but different. You get the idea.
Source Hendrik Lammers
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Here's a brown background pattern with subtle stripes. I hope you'll like the color. If not, feel free to change it using an image editor, if you know how of course. Personally, I'm using GIMP to create these backgrounds.
Source V. Hartikainen
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A free web background image with a seamless concrete-like texture and an Indian-red color.
Source V. Hartikainen
Prismatic Abstract Background Design
Source GDJ
This is so subtle: We’re talking 1% opacity. Get your squint on!
Source Atle Mo
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Square design drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
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
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I. Version with black background.
Source Firkin