A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
The base gradient edited so now more details are rendered.
Source Lazur URH
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Light and tiny, just the way you like it.
Source Rohit Arun Rao
This light yellow background pattern consists of an irregular pattern of spots. Here's a light background pattern with yellowish tint.
Source V. Hartikainen
First pattern tailor-made for Retina, with many more to come. All the old ones are upscaled, in case you want to re-download.
Source Atle Mo
Prismatic Groovy Concentric Background 3
Source GDJ
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Classic 45-degree pattern, light version.
Source Luke McDonald
Sharp pixel pattern, just like the good old days.
Source Paridhi
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
A version without colours blended together to give a different look.
Source Firkin
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin