"Polished Stone", Gray Background Pattern #1053
 Stone  CC BY-SA 3.0

A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).

Source V. Hartikainen

 More Textures
Floral design 100 (version 2, colour) #1772
 Green  CC 0

From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.

Source Firkin

Prismatic Abstract Geometric Background 2 #268
 Noise  CC 0

Prismatic Abstract Geometric Background 2

Source GDJ

Background pattern 26 (black) #199
 Dark  CC 0

Pattern formed from simple shapes. Black version.

Source Firkin

Light Aluminum #304
 Wall  CC BY-SA 3.0

Used correctly, this could be nice. Used in a bad way, all hell will break loose.

Source Atle Mo

Vintage pattern #1959
 Grid  CC 0

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

Source Firkin

Candyhole@2X #357
 Light  CC BY-SA 3.0

It’s a hole, in a pattern. On your website. Dig it!

Source Josh Green

Background pattern 306 (colour 5) #1879
 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

Colorful Floral Background 3 No Black #485
 Light  CC 0

Colorful Floral Background 3 No Black

Source GDJ

MBossed@2X #194
 Grid  CC BY-SA 3.0

Embossed lines and squares with subtle highlights.

Source Alex Parker