I really liked Vlad Zamfir's papers on "correct-by-construction" consensus protocols. What I love about this work is that it unifies traditional BFT consensus with blockchain consensus to make something better than both! Really exciting!
Abstract CBC: https://github.com/ethereum/research/blob/master/papers/cbc-...
Casper the friendly GHOST: https://github.com/ethereum/research/blob/master/papers/Casp...
I found the Abstract CBC paper a little easier to understand, as it goes into more detail about the correct-by-construction process.