I have a few more monsters in the pipeline (a Demon and Vampire).
But the next three in the release schedule is a Natural Caverns Tileset, World Map (overworld) Tileset, Deep Forest Tileset.
As for other assets from other creators, I'm not sure. I use the Pico-8 color palette, so searching for that might be the best way to go if you are looking for assets that match my style.