This one is quite simple in design, it consists of vertical stripes layered on top of a seamless texture.
Source V. Hartikainen
A seamless pattern formed from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Basic Pattern 2 No Background
Source GDJ
Retro Circles Background 4 No Black
Source GDJ
Prismatic Hypnotic Pattern 2 No Background
Source GDJ
Seamless Green Tile Background
Source V. Hartikainen
Background formed from the iconic plastic construction bricks that gave me endless hours of fun when I was a lad.
Source Firkin
A seamless pattern formed from a square tile based on a jpg on Pixabay. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin
Black And White Floral Pattern Background Inverse
Source GDJ
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Zero CC tileable grass texture, photographed and made by me. CC0
Source Sojan Janso
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
So tiny, just 7 by 7 pixels – but still so sexy. Ah yes.
Source Dmitriy Prodchenko
Produced using the clouds, flames and glass blocks plug-ins in Paint.net and the resulting .PNG vectorised with Vector Magic.
Source Firkin
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
Prismatic Groovy Concentric Background 2 No Black
Source GDJ