I may be mistaken, but I believe all core games from Gen 4 forward has post game content based on completing the national dex (though there are exclusions of mythical Pokemon). Emerald allows Chikorita, Cyndaquil or Totodile.
Diamond, Pearl, Platinum
Black, White, Heart Gold, Soul Silver, Black 2, White 2,
X, Y, Omega Ruby, Alpha Sapphire