Seamless tile 4 #1812
 Red  CC 0

Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern

Source Firkin

 More Textures
Whitey #109
 Light  CC BY-SA 3.0

A white version of the very popular linen pattern.

Source Ant Ekşiler

overlay crack #153
 Noise  CC 0

This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.

Source Lazur URH

Seamless Prismatic Quadrilateral Line Art Pattern No Background #379
 Diamond  CC 0

Seamless Prismatic Quadrilateral Line Art Pattern No Background

Source GDJ

Background pattern 214 (colour 3) #2375
 Green  CC 0

A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.

Source Firkin

Brushed Alum Dark@2X #66
 Dark  CC BY-SA 3.0

Because I love dark patterns, here is Brushed Alum in a dark coating.

Source Tim Ward

Background pattern 306 (colour 3) #1880
 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

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

Prismatic Groovy Concentric Background 3 #457
 Noise  CC 0

Prismatic Groovy Concentric Background 3

Source GDJ

Square ornament 38 #2147
 Dark  CC 0

From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.

Source Firkin

Paisley Background@2X #496
 Light  CC 0

Paisley Background

Source GDJ

Cubes@2X #134
 Light  CC BY-SA 3.0

This reminds me of Game Cube. A nice light 3D cube pattern.

Source Sander Ottens

Background pattern 306 #1882
 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

Prismatic Curved Diamond Pattern 8 No Background #549
 Dark  CC 0

Prismatic Curved Diamond Pattern 8 No Background

Source GDJ

Background pattern 328 (colour 2) #1800
 Green  CC 0

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

Source Firkin