The fight between Shinichi and the Parasite who took over his mother's body. Made even more awesome in the anime, thanks to the music playing during the scene, HYPNOTYK.
Everytime you hear HYPNOTIK in the anime, you know that awesomeness will ensue.
The new, stronger Shinichi completely owning Kana's jealous boyfriend Mitsuo when the latter picks a fight with him again after Shinichi's return in both the manga and anime.
Shinichi saving Satomi during Hideo's rampage, followed by him taking out Hideo by throwing a rock through his heart hundreds of meters away.
Shinichi avenging Kana by ripping out the Parasite's heart with one punch. With his human hand.
Despite being outnumbered 3 to 1 by physcially stronger opponents, Tamura managed to win by strategically taking down her parasite opponents one by one with only half her mind for most of the battle too.
While Shinichi goes into a panic when Gotoh escapes city hall and appears just meters away from him, Detective Hirama calmly takes aim and empties his pistol at the spot where Gotoh's heart would have been.