There is also the three legendary pattern
Kanto: Articuno, Zapdos, Moltres
Johto: Entei, Raikou, Suicune
Hoenn: Regirock, Registeel, Regice (Debate: There is now Regiggas in Sinnoh) and Groudon, Kyogre, and Rayquaza (look on Bulbapedia, go to origion and see, all relate)
Sinnoh: Mesprit...