The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
A free seamless background image with a texture of dark red "canvas". It should look very nice on web sites.
Source V. Hartikainen
The tile can be had by selecting the rectangle in Inkscape and using shift+alt+i. Remixed from a drawing in 'Flowers of Song', Frederick Weatherly, 1895.
Source Firkin
From a design in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
Vertical lines with a bumpy, yet crisp, feel to it.
Source Raasa
Bright Multicolored Floral Background by Karen Arnold from PDP.
Source GDJ
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
It’s an egg, in the form of a pattern. This really is 2012.
Source Paul Phönixweiß
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
Could be paper, could be a Polaroid frame – up to you!
Source Chaos
A re-make of the Gradient Squares pattern.
Source Dimitar Karaytchev
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
I love cream! 50x50px and lovely in all the good ways.
Source Thomas Myrman
Zero CC tileable cork floor, photographed and made by me. CC0
Source Sojan Janso
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
A fun-looking elastoplast/band-aid pattern. A hint of orange tone in this one.
Source Josh Green
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Colorful Floral Background No Black
Source GDJ
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin