To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Turn your site into a dragon with this great scale pattern.
Source Alex Parker
Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.
Source Firkin
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The image is a seamless pattern of a fishnet.
Source Yamachem
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
Zero CC tileable hard cover green book, scanned and made by me. CC0
Source Sojan Janso
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
Nothing like a clean set of bed sheets, huh?
Source Badhon Ebrahim
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
Colored maple leaves scattered on a surface. This is tileable, so it can be used as a background or wallpaper.
Source Eady
Colour version that is close to the original drawing uploaded to Pixabay by pencilparker.
Source Firkin
This light yellow background pattern consists of an irregular pattern of spots. Here's a light background pattern with yellowish tint.
Source V. Hartikainen
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
A seamless paper background colored in pale yellow.
Source V. Hartikainen