From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
Derived from elements found in a floral ornament drawing on Pixabay.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A seamlessly tile-able grunge background image.
Source V. Hartikainen
This was formed by distorting an image of a background on Pixabay.
Source Firkin
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
A dark metallic background with a pattern of stamped dots. Here's a dark "metallic" background pattern for you.
Source V. Hartikainen
Clover with background for St. Patrick's Day. Add to a card with a doily, ribbon, a leprechaun or other embellishments.
Source BAJ
ZeroCC tileable wood boards texture, photographed and made by me. CC0
Source Sojan Janso
Prismatic Groovy Concentric Background 3
Source GDJ
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
Redrawn based on a drawing in 'По Сѣверо-Западу Россіи' Konstantin Sluchevsky, 1897.
Source Firkin
Prismatic Chevrons Pattern 5 With Background
Source GDJ
Similar to original, but without gaps in between the arrows. This seamless pattern was created from a rectangular tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
Wild Oliva or Oliva Wilde? Darker than the others, sort of a medium dark pattern.
Source Badhon Ebrahim
Derived from a drawing in 'Elfrica. An historical romance of the twelfth century', Charlotte Boger, 1885
Source Firkin
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
Dark blue concrete wall with some small dust spots.
Source Atle Mo