From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Tiny little flowers growing on your screen. Nice, huh?
Source Themes Tube
A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
Hexagonal dark 3D pattern. What more can you ask for?
Source Norbert Levajsics
This is the remix of an OCAL clipart called "Art Nouveau ornament" uploaded by "microcosme".Thanks.This is a seamless pattern of an Art Nouveau ornament.
Source Yamachem
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin