The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees
Derived from an image that was uploaded to Pixabay by TheDigitalArtist
Source Firkin
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
An abstract texture of black metal pipes (seamless).
Source V. Hartikainen
A free tileable background colored in off-white (antique white) color.
Source V. Hartikainen
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
A version without colours blended together to give a different look.
Source Firkin
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
Not the Rebel alliance, but a dark textured pattern.
Source Hendrik Lammers
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Light square grid pattern, great for a “DIY projects” sort of website, maybe?
Source Rafael Almeida
A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin