A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
Some rectangles, a bit of dust and grunge, plus a hint of concrete.
Source Atle Mo
Prismatic Curved Diamond Pattern No Background
Source GDJ
Pattern produced in Paint.net using the Vibrato plug-in.
Source Firkin
The name tells you it has curves. Oh yes, it does!
Source Peter Chon
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
This one is super crisp at 2X. Lined paper with some dust and scratches.
Source HQvectors
Super dark, crisp and detailed. And a Kill Bill reference.
Source Badhon Ebrahim
Vertical lines with a bumpy, yet crisp, feel to it.
Source Raasa
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Might not be super subtle, but quite original in its form.
Source Alex Smith
Remixed from a drawing in 'A Girl in Ten Thousand', Elizabeth Meade, 1896.
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Dark pattern with some nice diagonal stitched lines crossing over.
Source Ashton
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Zero CC tileable seed texture, edited by me to be seamless from a Pixabay image. CC0
Source Sojan Janso
Prismatic Curved Diamond Pattern 5 No Background
Source GDJ
White circles connecting on a light gray background.
Source Mark Collins
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
Remixed from a drawing in 'Analecta Eboracensia', Thomas Widdrington, 1897.
Source Firkin
Awesome name, great pattern. Who does not love space?
Source Nick Batchelor
Number five from the same submitter, makes my job easy.
Source Dima Shiper