Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Sharp pixel pattern, just like the good old days.
Source Paridhi
Zero CC tileable seed texture, edited by me to be seamless from a Pixabay image. CC0
Source Sojan Janso
Prismatic Hexagonalism Pattern No Background
Source GDJ
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
Colorful Floral Background 3 No Black
Source GDJ
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
Stefan is hard at work, this time with a funky pattern of squares.
Source Stefan Aleksić
Retro Circles Background 7 No Black
Source GDJ
From a drawing in 'Bond Slaves. The story of a struggle.', Isabella Varley, 1893.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Zero CC tileable bark texture, photographed and made by me. CC0
Source Sojan Janso
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A seamless pattern formed from miutopia's cakes on a tablecloth.
Source Firkin
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
Lovely pattern with splattered vintage speckles.
Source David Pomfret
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
It’s a hole, in a pattern. On your website. Dig it!
Source Josh Green
Prismatic 3D Isometric Tessellation Pattern 6
Source GDJ
Formed by heavily distorting part of a an image of a fish uploaded to Pixabay by GLady
Source Firkin
A repeating background of beige paper with vintage look. Repeats to infinity, as usual.
Source V. Hartikainen