Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
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 seamless pattern with a unit cell drawn as a bitmap in Paint.net and vectorized in Vector Magic.
Source Firkin
This light background pattern has a texture of "frozen" surface with diagonal stripes. Here's an yet another addition to the collection of free website backgrounds.
Source V. Hartikainen
Zero CC bark from fur tree tileable texture, photographed and made by me. CC0
Source Sojan Janso
Clean and crisp lines all over the place. Wrap it up with this one.
Source Dax Kieran
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
A pale olive green background with a seamless texture.
Source V. Hartikainen
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i
Source Firkin
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
A frame using leaves from an image that was uploaded to Pixabay by mayapujiati
Source Firkin
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
A seamless pattern with wide vertical stripes colored in pale yellow.
Source V. Hartikainen
Abstract Ellipses Background Grayscale
Source GDJ
Black brick wall pattern. Brick your site up!
Source Alex Parker
If you’re sick of the fancy 3D, grunge and noisy patterns, take a look at this flat 2D brick wall.
Source Listvetra
This is a seamless pattern which is derived from a flower petal image.
Source Yamachem
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Prismatic Chevrons Pattern 5 With Background
Source GDJ