Bitcoin (of course)
Ethereum Yellow Paper
PBFT
Raft
Paxos
BFT-Smart
Zyzzyva
HoneybadgerBFT
500BFT
Kafka (not a BFT but worth reading)
OmniLedger (and Byzcoin)
Zerocash
PoS (Ouroboros)
Snowwhite
Hybrid Consensus
UC model (for cryptographic protocol proofs)
Sleepy Model of Consensus
Town crier
SGX Papers (3 white papers by Intel)
Bitcoin-NG
SmartCast
SoK: Research Perspectives and Challenges for Bitcoin and Cryptocurrencies (a nice SoK)
Solidus
Algorand
Solida
FLP and CAP (and their differences)
Rethinking large-scale consensus
Fruitchains
Hawk: The blockchain model of cryptography and privacy-preserving smart contracts
BlockDAG
TumbleBit
Tesseract: real time cryptocurrency exchange with trusted hardware
arXiv 1602.06997
Solida
arXiv 1704.02397
SoK: Consensus in the Age of Blockchains