From a drawing in 'Kingsdene', Maria Fetherstonehaugh, 1878.
Source Firkin
Sometimes you just need the simplest thing.
Source Fabricio
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
Prismatic Abstract Line Art Pattern Background
Source GDJ
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Zero CC tileable hard cover green book, scanned and made by me. CC0
Source Sojan Janso
Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.
Source Ivan Ginev
Sort of like the back of a wooden board. Light, subtle, and stylish, just the way we like it!
Source Nikolalek
Prismatic Rounded Squares Grid 4 No Background
Source GDJ
I skipped number 3, because it wasn’t all that great. Sorry.
Source Dima Shiper
Prismatic Snowflakes Pattern No Background
Source GDJ
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin