Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Prismatic Floral Background No Black
Source GDJ
Remixed from a drawing in 'Incidents on a Journey through Nubia to Darfoor', F. Ensor, 1891.
Source Firkin
A repeating background of thick textured paper. Actually, it turned out to look like something between a paper and fabric.
Source V. Hartikainen
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
This ladies and gentlemen, is texturetastic! Love it.
Source Adam Pickering
A very dark asfalt pattern based off of a photo taken with my iPhone.
Source Atle Mo
A seamless pattern formed from miutopia's cakes on a tablecloth.
Source Firkin
Prismatic Hexagonalist Pattern No Background
Source GDJ
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
A colourful background drawn originally in paint.net and vectorised in Vector Magic.
Source Firkin
Abstract Ellipses Background Grayscale
Source GDJ
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
Seamless Green Tile Background
Source V. Hartikainen
Just the symbols of the signs of the zodiac distributed in a chequer board-like pattern
Source Firkin
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Abstract Tiled Background Extended 10
Source GDJ