Dragonball - Probably one of the Goku vs Jackie Chun fights, or the last episode in the Goku vs Piccolo fight right at the end of Dragonball.
Dragonball Z - Either the episode where Goku went SSJ for the first time, Vegeta went USSJ for the first time, Gohan went SSJ2 for the first time, or Goku went SSJ3 for the first time. They were all AWESOME for their own reasons. First was emotional because they thought Krillen couldn't be revived, and Frieza was unbeatable, and they finally confirmed the myth of the SSJ legend. Gohan changing was also very emotional and incredible badass, he became so powerful and destroyed Cell and the Mini Cells in one hit, it was just so awesome. Vegeta became a massive badass when he went USSJ for the first time and suddenly pumped all his muscles up, and started pounding on Cell. And the buildup to SSJ3 was amazing, and then the music, and the look was great.
Only other episode I can think of was when Vegeta sacrificed himself against Buu, well actually there are others I can think of, boy I loved DBZ back in the day.
Dragonball GT - The last episode, because it meant the end of this piece of ****. Ruined the good name of Dragonball, wasn't even made by AT, awful stuff.