The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Nicely executed tiling for an interesting pattern.
Source Ignasi Àvila Padró
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!
Source V. Hartikainen
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
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
Prismatic Polyskelion Pattern No Background
Source GDJ
ZeroCC tileable moss texture, photographed and made by me. CC0
Source Sojan Janso
Prismatic Curved Diamond Pattern 5 No Background
Source GDJ
A criss-cross pattern similar to one I saw mown into a sports field.
Source Firkin
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Nothing like a clean set of bed sheets, huh?
Source Badhon Ebrahim
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
From a drawing in 'Hundert Jahre in Wort und Bild', S. Stefan, 1899.
Source Firkin
The image a seamless pattern of a wire-mesh fence.I want you to use this pattern as a lower layer.
Source Yamachem
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
Lovely light gray floral motif with some subtle shades.
Source GraphicsWall
It was called Navy Blue, but I made it dark. You know, the way I like it.
Source Ethan Hamilton
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin