CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
A simple but elegant classic. Every collection needs one of these.
Source Christopher Burton
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
From an image on opengameart.org shared by rubberduck.
Source Firkin
Utilising a bird from s-light and some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
A black tile-able background with paper-like texture.
Source V. Hartikainen
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
Lovely light gray floral motif with some subtle shades.
Source GraphicsWall
Light and tiny, just the way you like it.
Source Rohit Arun Rao
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
Derived from a drawing in 'Historiske Afhandlinger', Adolf Jorgensen, 1898.
Source Firkin
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Paper pattern with small dust particles and 45-degree strokes.
Source Atle Mo
Abstract Stars Geometric Pattern Prismatic No Background
Source GDJ
This is a seamless pattern which is derived from a flower petal image.
Source Yamachem
This yellow background consists of a pattern of glossy gold buttons arranged in polka dot style on a seamless texture. Here's a pale yellow background pattern. Feel free to use it for your needs!
Source V. Hartikainen
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo
Zero CC tileable dry grass texture, photographed and made by me. CC0
Source Sojan Janso