Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
White circles connecting on a light gray background.
Source Mark Collins
Lovely light gray floral motif with some subtle shades.
Source GraphicsWall
One more in the line of patterns inspired by Japanese/Asian styles. Smooth.
Source Kim Ruddock
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
This was formed by distorting an image of a background on Pixabay.
Source Firkin
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Same as Silver Scales, but in black. Turn your site into a dragon with this great scale pattern.
Source Alex Parker
By popular request, an outline version of the pentagon pattern.
Source Atle Mo
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
Prismatic Floral Background No Black
Source GDJ
From a drawing in 'Royal Ramsgate', James Simson, 1897.
Source Firkin
Here's an yet another seamless note paper texture for use as a background on websites.
Source V. Hartikainen
You could get a bit dizzy from this one, but it might come in handy.
Source Dertig Media
Not the Rebel alliance, but a dark textured pattern.
Source Hendrik Lammers
Because I love dark patterns, here is Brushed Alum in a dark coating.
Source Tim Ward
The texture of this background image has some similarities with leather, and it's colored in a dark brown color. So, if you are looking for a dark brown background image for your website, this may be an option for you.
Source V. Hartikainen
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
A seamless pattern of leopard skin. It should look nice as a background element on web pages.
Source V. Hartikainen