Someone should start a list....
2:1 rolling ball diamond ratio
sliding ball system, 70% of the mirror distance
Corner-5
Plus system (AKA plus-2)
constructing a mirror target
"Opposite-3" kicking (magic spot on a pool table)
Max side spin systems
Graduated side spin system (1 tip = 1 diamond, sort of)
short, soft kick, ball close to cushion, shallow into cushion
short, stun kick, ball close to cushion, shallow into cushion
System Sid (end rail first to hit on side rail)
Mosconi's crossing line intersection construction (not very good)
Specific reference lines for special shots, such as two rails (long, head) banking from the foot spot at one pocket