Mine are...
RRK --> The whole Shishio Arc. I love how this arc's played out, both in anime and manga.
DB ---> That episode where Goku first became Super Saiyajin. I think it's the Freeza Arc
Hikaru no Go ---> Episode 01 - 03, that whole Hikaru meet Akira episodes, cute Episodes 60-64 where Sai disappeared,
tragic.
fma --> Episode 03, when Ed and Al were reviving their Mom, the story as well as the action behind it almost made me
cry. Last episode.
Naruto --> That Naruto and Kiba fight. When Naruto first summoned Gamabunta. The three Sannins fight. First time
Team 7 encountered Orochimaru. Fight between Naruto and Gaara.
Prince of Tennis --> Chibi episodes, just because they're cute.
Gundam Seed --> That episode where Athrun decided to fight alongside Kira.
Gundam Seed Destiny --> .(so far...) Episode 08. Athrun's proposal clinched it ^^
Gundam Wing --> Last three episodes
Slamdunk --> Shohoku vs. Ryonan.
Yami no Matsuei --> Kyoto Arc.. Episodes 10-13