Horizontal and vertical lines on a light gray background.
Source Adam Anlauf
Prismatic Geometric Tessellation Pattern No Background
Source GDJ
A free seamless background texture that looks like a brown stone wall.
Source V. Hartikainen
A lovely light gray pattern with stripes and a dash of noise.
Source V. Hartikainen
From a drawing in 'Danmarks Riges Historie af J. Steenstrup, Kr. Erslev, A. Heise, V. Mollerup, J. A. Fridericia, E. Holm, A. D. Jørgensen', 1897.
Source Firkin
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
Prismatic Hexagonalism Pattern No Background
Source GDJ
I love cream! 50x50px and lovely in all the good ways.
Source Thomas Myrman
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Fix and cc0 to get the tile this is based on.
Source SliverKnight
No relation to the band, but damn it’s subtle!
Source Thomas Myrman
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
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
A free grid paper background pattern for using on web sites.
Source V. Hartikainen
CC0 and seamless wellington boot pattern.
Source SliverKnight
Black And White Floral Pattern Background Inverse
Source GDJ
Prismatic Chevrons Pattern 5 With Background
Source GDJ
Prismatic 3D Isometric Tessellation Pattern 6
Source GDJ
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin