Before I started to feel like boosted experience was a cheap shortcut to getting high level Pokémon, I actually raised a good number of level 100s. Sadly, with no breeding many Pokémon were only obtainable by trading. Eventually I caught on to the idea of raising all the way to level 100 on alternate versions before trading over to Red. In more recent times I've returned to finish raising some of my higher level boosteds, just for fun.
Mewtwo Level 100
Scyther Level 100
Jolteon Level 100
Eevee Level 100
Kabutops Level 100
Flareon Level 100
Charmander Level 100
Venusaur Level 100
Articuno Level 100
Ponyta Level 100
Blastoise Level 100
Venusaur Level 100
Victreebel Level 100
Bulbasaur Level 100
Squirtle Level 100
Charmeleon Level 100
Wartortle Level 100
Ivysaur Level 100
Notes:
- These are my Kanto generation Pokémon that were raised with boosted experience. For the rest, click here.