So many...
The Terry Shaivo episode was great..
The Episode where they did a take off of anime and the kids all had ninja weapons was great..
But I think my all time favorite, was the episode where a hippy jam festival popped up in southpark, and cartman had to drill to the center of the concert and plug a slayer CD into the sound system and play "Reign of Blood" to get them to disperse, thereby saving southpark
