People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay
Prismatic Triangular Background Design Mark II 5
Source GDJ
From a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
A chequerboard pattern with a fruit theme. The fruits are from a posting by inkscapeforum.it.
Source Firkin
Prismatic Geometric Pattern Background 2
Source GDJ
Wasn't satisfied with the original's colouring. Too much component transfer and colormatrixes yet the results are lacking a bit. So this time it is a simple black to transparent fade, making it possible remixing easily once there will be other blending modes supported as well. Probably in inkscape 0.92.
Source Lazur URH
I know there is one here already, but this is sexy!
Source Gjermund Gustavsen
Same as Silver Scales, but in black. Turn your site into a dragon with this great scale pattern.
Source Alex Parker
Looks like an old wall. I guess that’s it then?
Source Viahorizon
The image depicts meshed silhouettes of various things.The original image is an OCAL clipart called "Enter FOSSASIA 2016 #IoT T-shirt Design Contest" uploaded by "openclipart".Thanks.
Source Yamachem
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
Can’t believe we don’t have this in the collection already! Slick woven pattern with crisp details.
Source Max Rudberg
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
Remixed from an image that was uploaded to Pixabay by CatherineClennan
Source Firkin
Wild Oliva or Oliva Wilde? Darker than the others, sort of a medium dark pattern.
Source Badhon Ebrahim
Did anyone say The Hoff? This pattern is in no way related to Baywatch.
Source Josh Green
A light background pattern with diagonal stripes. Here's a simple light striped background for you.
Source V. Hartikainen
Zero CC tileable grass texture, photographed and made by me. CC0
Source Sojan Janso
Found on the ground in french cafe in kunming, Yunnan, china
Source Rejon
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
This is a remix of "blue wave-seigaiha".I hope this subtle color version of Seigaiha would be suitable for background .
Source Yamachem
Number five from the same submitter, makes my job easy.
Source Dima Shiper
Number 3 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos