Your FAVORITE Saga/Arch/Season of an Anime

What are some of your favorite sagas of any anime?

For me, my absolute favorite saga is The Chapter Black Saga from Yu Yu Hakusho.

I also like the Sasuke Retrieval arch from Naruto, and the Android Saga from Dragonball Z.

i really like the orochimaru invasion in Naruto. in dbz its got to be the frieza and cell sagas.