From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
This is sort of fresh, but still feels a bit old school.
Source Martuchox
Prismatic Hexagonalism Pattern No Background
Source GDJ
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
This one needs to be used in small areas; you can see it repeat.
Source Luca
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
Prismatic Abstract Line Art Pattern Background 2
Source GDJ
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
A seamless background texture of old cardboard.
Source V. Hartikainen
Some more diagonal lines and noise, because you know you want it.
Source Atle Mo
A very dark spotted twinkle pattern for your twinkle needs.
Source Badhon Ebrahim
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
This was formed by distorting an image of a background on Pixabay.
Source Firkin
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Here's an yet another seamless note paper texture for use as a background on websites.
Source V. Hartikainen
Beautiful dark noise pattern with some dust and grunge.
Source Vincent Klaiber
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay