Just started my journey through some of these, so fair warning. But I believe them to be valuable contributions so far.
Leviathan by Hobbes of course.
An Open Letter to Open-Minded Progressives by Moldbug. Does a very good job exposing and tearing down the worldview that has been popular since the French Revolution.
The Dark Enlightenment by Nick Land. Err, well, the first half or so of it anyway. I find all of part four wanders pretty aimlessly and comes to a silly conclusion, but the rest of it is very good.
Just a note though, that especially the last two also focus on traditionalism and debunking the idea of equality, so they aren't purely monarchist works. More neo-reactionary, which tends to advocate monarchism anyway.