From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Actually, there's no clouds in it, but I think it looks quite nice.
Source V. Hartikainen
A seamless web background with texture of aged grid paper.
Source V. Hartikainen
A gray background pattern with a texture of textile. Suits perfectly for web design.
Source V. Hartikainen
One more in the line of patterns inspired by Japanese/Asian styles. Smooth.
Source Kim Ruddock
You could get a bit dizzy from this one, but it might come in handy.
Source Dertig Media
Tiny circle waves, almost like the ocean.
Source Sagive
Remixed from a JPG that was uploaded to Pixabay by susanlu4esm
Source Firkin
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
Prismatic Curved Diamond Pattern 8 No Background
Source GDJ
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo
Retro Circles Background 8 No Black
Source GDJ
A seamless design of flowers remixed from a jpg on Pixabay by Prawny.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A rusty grunge background for websites. Feel free to use it in your site's theme.
Source V. Hartikainen
A version without colours blended together to give a different look.
Source Firkin
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
You know I’m a sucker for these. Well-crafted paper pattern.
Source Mihaela Hinayon
Can never have too many knitting patterns, especially as nice as this.
Source Victoria Spahn