I pretty much only know about Generation I and a bit of Generation II; Pokémon brings back great memories of my childhood. Pokémon Yellow is probably my favorite Gameboy game, I love how closely it follows the anime series. I also enjoyed Pokémon Red and Blue and Pokémon Gold. Squirtle is probably my favorite Pokémon and my others include most of the classics and their evolved forms: Pikachu, Charmander, Bulbasaur, Growlithe, Alakazam and a few Generation II Pokémon such as Typhlosion and Ampharos; really, the list could go on and on.
I haven't watched it much recently, I'm about five generations behind, but I still get quite nostalgic when I think of Pokémon. Gotta Catch 'Em All will forever be burned into my memory.