Please comment with some of the concepts or techniques you've seen. I will start the list:

Write ahead logging
SSL passthrough / termination on load balancers
Clock vectors
Hinted handoff
Bloom filters
Quad trees
Gossip protocols
Merkle trees
Isolation levels (read uncomitted, read comitted, repeatable read, serializable)
Paxos algorithm
Two phase commit
Two phase locking
Consistent hashing