Best noir films to study and learn the genre?

I've always loved film noir, and recently I started to dive deep into watching and taking notes on some of the classics of the genre to better understand what makes a good noir film. As I've been doing this, I've been left to wonder: what are the best noir films to learn the genre?

So really, what are some of your favorite noir film(s)? What do these film(s) do differently that others don't? And what can we learn from said film(s)?