Triangles@2X #128
 Dark  CC BY-SA 3.0

Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.

Source Ivan Ginev

 More Textures
Retro Squares Background 7 #397
 Noise  CC 0

Retro Squares Background 7

Source GDJ

Background pattern 306 (colour 6) #1878
 Colorful  CC 0

Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.

Source Firkin

Checkered Light Emboss #280
 Grid  CC BY-SA 3.0

Sort of like the Photoshop transparent background, but better!

Source Alex Parker

Colourful background #2011
 Colorful  CC 0

Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic

Source Firkin

Prismatic Arrows Background #392
 Noise  CC 0

Prismatic Arrows Background

Source GDJ

Background pattern green #1953
 Green  CC 0

To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.

Source Firkin

fawn spot pattern #2472
 Dark  CC 0

The image depicts a Japanese Edo pattern called "kanoko or 鹿の子" meaning "fawn" which has a fur with small white spots.

Source Yamachem

Fleurs-de-lys pattern 2 (colour) #2204
 Colorful  CC 0

Colour version of the original pattern inspired by the front cover of 'Old and New Paris', Henry Edwards, 1894.

Source Firkin

Background pattern 269 #2062
 Dark  CC 0

A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i

Source Firkin

Gun Metal #360
 Dark  CC BY-SA 3.0

With a name this awesome, how can I go wrong?

Source Nikolay Boltachev

“Transparent” Background Pattern #493
 Light  CC 0

An emulated “transparent” background pattern, like that of all kinds of computer graphics software.

Source AdamStanislav

Floral design 91 #1814
 Dark  CC 0

From a drawing in 'Hubert Montreuil, or the Huguenot and the Dragoon', Francisca Ouvry, 1873.

Source Firkin