A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
Prismatic Groovy Concentric Background 3
Source GDJ
A large pattern with funky shapes and form. An original. Sort of origami-ish.
Source Luuk van Baars
This background pattern contains a seamless texture of bark. It's not very realistic, but I think it looks quite nice.
Source V. Hartikainen
Basket Fibers, Basket Texture, Braid Background style CC0 texture.
Source 1A-Photoshop
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 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Love the style on this one, very fresh. Diagonal diamond pattern. Get it?
Source INS
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
A new one called white wall, not by me this time.
Source Yuji Honzawa
Square design drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Everyone loves a diamond, right? Make your site sparkle.
Source AJ Troxell
A light gray background pattern with seamless fabric-like texture and almost unnoticeable stripes.
Source V. Hartikainen
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo