It depends on what starter I choose.
If I choose Chikorita:
Politoad (or Corsola), Houndoom, Noctowl, Ampharos, Espeon.
If I choose Cyndaquil:
Jumpluff, Umbreon, Noctowl, Lanturn, Sneasel.
If I choose Tododile:
Houndoom, Jumpluff (or Bellossom or Sunflora), Noctowl, Ampharos, Espeon.
(Since my Azumarill, Gyarados, Vaporeon, Mr. Mime, Gengar, and Dragonite are all level 80 or higher in my Platinum, I won't be using these in Heart Gold or Soul Silver.)
Alternate Pokemon: Stantler (Never have used him.) Aipom (maybe), Larvitar (idk), Sudowoodo (B/c Rock moves are super effective against Ice Types.)