Ampharos is cool and easily available.
Heracross is cool and not easily available. I'll still catch a Heracross and feel damn cool I own one since it's so rare.
New Bark Town
>Chikorita/Bayleef/Meganium
>Cyndaquil/Quilava/Typhlosion
>Totodile/Croconaw/Feraligtr
Route 29
>Sentret/Furret
>Hoothoot/Noctowl
Route 30
>Ledyba/Ledian
>Spinarak/Ariados
Dark Cave
>Crobat (evolve Zubat/Golbat)
>Dunsparce
Ruins of Alph
>Unown
Violet City
>Togepi/Togetic
Route 32
>Mareep/Flaaffy/Ampharos
>Hoppip/Skiploom/Jumpluff
>Wooper/Quagsire
>Qwilfish (swarm with Old Rod)
Slowpoke Well - King's Rock held by wild Slowpoke
>Politoed (catch Poliwag earlier with Old Rod)
>Slowking
Ilex Forest - obtain TM02 Headbutt
>Aipom
>Pineco/Forretress
>Heracross
Goldenrod City
>Espeon
>Umbreon
Route 35
>Yanma
National Park
>Bellossom
>Sunkern/Sunflora
Route 36
>Stantler
>Sudowoodo
That's 45 possible Gen II Pokémon before reaching Ecruteak City, where the game opens up more with letting you choose to go east or west, getting Surf for backtracking, getting the Good Rod in Cianwood, thr Burned Tower, etc. Suddenly Natu/Xatu, Smeargle, Raikou, Entei, Suicune, Steelix and Scizor (wild Magnemite can hold Metal Coat), Miltank, Girafarig, Mantine, Corsola, etc. become available.
