A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
Remixed from a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Remixed from a drawing in 'Line and form", Walter Crane, 1914.
Source Firkin
Lovely pattern with splattered vintage speckles.
Source David Pomfret
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Number 3 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Love the style on this one, very fresh. Diagonal diamond pattern. Get it?
Source INS
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Colour version that is close to the original drawing uploaded to Pixabay by pencilparker.
Source Firkin
The image depicts a seamless pattern of pine tree leaves.
Source Yamachem
A new take on the black linen pattern. Softer this time.
Source Atle Mo
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
From a drawing in 'Hyde Park from Domesday-Book to date', John Ashton, 1896.
Source Firkin
Sharp diamond pattern. A small 24x18px tile.
Source Tom Neal