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

 More Textures
Tessellation 16 (colour 2) #2214
 Colorful  CC 0

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

Source Firkin

Background pattern #1942
 Brown  CC 0

Formed by distorting an image on Pixabay that was uploaded by gustavorezende. To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.

Source Firkin

Abstract Tiled Background Extended 9 #520
 Dark  CC 0

Abstract Tiled Background Extended 9

Source GDJ

Background pattern 117@2X #525
 Noise  CC 0

A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.

Source Firkin

Background pattern 266 #2068
 Dark  CC 0

Remixed from a drawing in 'Some account of the Worshipful Company of Ironmongers', John Nicholl, 1866.

Source Firkin

Background pattern 215 #2371
 Brown  CC 0

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

Source Firkin

Dark Steel Grid Background Pattern #1081
 Metal  CC BY-SA 3.0

Here's a dark background pattern that contains a steel grid pattern as a texture. Use it as a website background or for other purposes. It's free!

Source V. Hartikainen

Prismatic Isometric Cube Wireframe Pattern No Background #499
 Light  CC 0

Prismatic Isometric Cube Wireframe Pattern No Background

Source GDJ

Vintage tile background (colour 3) #2246
 Green  CC 0

A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.

Source Firkin

Colorful Bicycles Background #207
 Noise  CC 0

Pixabay.

Source GDJ

Retro Squares Background 2@2X #417
 Noise  CC 0

Retro Squares Background 2

Source GDJ

Prismatic Groovy Concentric Background 4 #461
 Noise  CC 0

Prismatic Groovy Concentric Background 4

Source GDJ

Retro Squares Background 6 #396
 Noise  CC 0

Retro Squares Background 6

Source GDJ

Black And White Floral Pattern Background Inverse #196
 Dark  CC 0

Black And White Floral Pattern Background Inverse

Source GDJ

Background pattern 332 #1742
 Noise  CC 0

The tile this is formed from can be retrieved in Inkscape by selecting the rectangle and using shift+alt+i

Source Firkin

Configurable Graph Paper #141
 Stripes  CC BY-SA 3.0

Pass parameters to the URL or edit the source code variables to configure the graph paper for the division desired.

Source JayNick