From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A version without colours blended together to give a different look.
Source Firkin
Drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
From an image on opengameart.org shared by rubberduck.
Source Firkin
Fix and cc0 to get the tile this is based on.
Source SliverKnight
Prismatic Chevrons Pattern 5 With Background
Source GDJ
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Prismatic Basic Pattern 2 No Background
Source GDJ
Adapted from an image that was uploaded to Pixabay by Anerma.
Source Firkin
A free seamless background pattern for use on websites.
Source V. Hartikainen
Zero CC tileable yellow craft paper; scanned and made by me. CC0
Source Sojan Janso