Some of the highlights of DBZ were in my opinion:
(~) Episode 30 (first fight between Goku and Vegeta), episode 95 (Goku's first transformation into SSJ, as already mentioned), episode 184 (Gohan's first transformation into SSJ2) and around episode 285 (final battle, Buu's destruction).
I'm pretty sure there's a couple of other special moments, but that's all I recall right now.
(Note: The episode numbers refer to the original japanese version. )
a lot of these good episodes, like Vegeta sacrificing himself and Gohan going SSJ2, to me they were only good because of the American OST tracks which accompanied them. Good electric music =D