Background pattern 215 (colour 3) #2369
 Pink  CC 0

A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.

Source Firkin

 More Textures
Cardboard@2X #279
 Paper  CC BY-SA 3.0

A good starting point for a cardboard pattern. This would work well in a variety of colors.

Source Atle Mo

Floral design 70 #2520
 Dark  CC 0

Traced from a drawing in 'Household Stories from the Collection of the Brothers Grimm', Wilhelm Carl Grimm , 1882.

Source Firkin

Prismatic Rounded Squares Grid 4 No Background #491
 Noise  CC 0

Prismatic Rounded Squares Grid 4 No Background

Source GDJ

Always Grey #53
 Dark  CC BY-SA 3.0

Crossing lines with a subtle emboss effect on a dark background.

Source Stefan Aleksić

Geometric pattern #2003
 Grid  CC 0

A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i

Source Firkin

Retro Circles Background 5 #424
 Noise  CC 0

Retro Circles Background 5

Source GDJ

Background pattern 10 #216
 Noise  CC 0

A pattern drawn in Paint.net and vectorized in Vector Magic.

Source Firkin

Diamond pattern (colour 2) #2284
 Green  CC 0

From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.

Source Firkin

Vintage pattern #1957
 Grid  CC 0

Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.

Source Firkin

Xv@2X #315
 Paper  CC BY-SA 3.0

Floral patterns will never go out of style, so enjoy this one.

Source Lasma

Abstract Tiled Background Extended 8 #519
 Noise  CC 0

Abstract Tiled Background Extended 8

Source GDJ

Floral pattern 7 (colour 5) #2287
 Green  CC 0

Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.

Source Firkin

Prismatic Groovy Concentric Background 4@2X #462
 Noise  CC 0

Prismatic Groovy Concentric Background 4

Source GDJ