80-90, although I will edit this answer when I find exact numbers.
EDIT: Pikachu, lv88 / lapras, lv80 / snorlax, lv82 / venasaur, charizard, and blastoise, all lv 84
Suicune is at Level 40 in HeartGold and SoulSilver.
By training your Pokemon.
breed it
Level 18
Level 20.
level 30
level 28
lugia is level 45.
Level 55
You must "endlessly" train your Pokemon.
56 to 63
Level 25.