Tiny circle waves, almost like the ocean.
Source Sagive
Remixed from a drawing that was uploaded to Pixabay by captenpub.
Source Firkin
Prismatic Abstract Background Design No Black
Source GDJ
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A bit simplified version. Although it could be edited out to be simpler. Anyway, this time the tiling is converted to a pattern fill -which is using clipping for the tile's edges.
Source Lazur URH
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
Clover with background for St. Patrick's Day. Add to a card with a doily, ribbon, a leprechaun or other embellishments.
Source BAJ
The image is a design of blue glass.How about using it as background image?
Source Yamachem
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
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
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
A simple but elegant classic. Every collection needs one of these.
Source Christopher Burton
I guess this is inspired by the city of Ravenna in Italy and its stone walls.
Source Sentel
Pattern Background, Texture, Photoshop Structure style CC0 texture.
Source Darkmoon1968
The image depicts a seamless pattern of a Japanese family crest called "chidori" in Japanese .A chidori in Japanese means a plover in English.
Source Yamachem
Non-seamless pattern drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
To get the tile this is made up from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remix from a drawing in 'Ostatnie chwile powstania styczniowego', Zygmunt Sulima, 1887.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Derived from a PNG that was uploaded to Pixabay by nutkitten
Source Firkin
A version without colours blended together to give a different look.
Source Firkin
A free light orange brown wallpaper with vertical stripes designed for use as a tiled background on websites. An yet another background pattern with vertical stripes.
Source V. Hartikainen