Distributed systems theory for the distributed systems engineer
(Before you down vote: I have a PhD in distributed systems and fault tolerance. Okay, now you can down vote for the duchebaggery of this prescript)I think a fundamental and very underrated paper and concept (which actually predates Paxos, yet Lamport ignored or was unaware of) is the notion of randomized consensus protocols. Simpler than "structured" leader type algorithms. Believe Ben Or's algorithm was first.