I took the liberty of using Dmitry’s pattern and made a version without perforation.
Source Atle Mo
Prismatic Groovy Concentric Background
Source GDJ
Awesome name, great pattern. Who does not love space?
Source Nick Batchelor
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Real snow that tiles, not easy. This is not perfect, but an attempt.
Source Atle Mo
Same as the black version, but now in shades of gray. Very subtle and fine grained.
Source Atle Mo
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Awesome name, great pattern. Who does not love space?
Source Nick Batchelor
Green Background Pattern
Source V. Hartikainen
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
You know I love paper patterns. Here is one from Stephen. Say thank you!
Source Stephen Gilbert
This one is something special. I’d call it a flat pattern, too. Very well done, sir!
Source GetDiscount
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Remixed from a vector adapted from a jpg on Pixabay. The tile this is constructed from can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Prismatic Snowflakes Pattern 3 No Background
Source GDJ
Just what the name says, paper fibers. Always good to have.
Source Heliodor jalba
Black And White Floral Pattern Background Inverse
Source GDJ
The image depicts a Japanese Edo pattern called "kanoko or 鹿の子" meaning "fawn" which has a fur with small white spots.
Source Yamachem
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
The image is a seamless pattern of a fishnet.
Source Yamachem
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin