Ohh.. The episode with the YouTube "celebs".. The contest of the biggest turd, with Bono from U2 by the end.. ^^

The best thing about South Park: Chinpokomon.

The image of God when he appears before the South Park citizens http://25.media.tumblr.com/tumblr_lo9g34fHSv1qh0knpo1_500.jpg

"Whoa dude, I just saw Tony Danza!"

This scene from the South Park movie has a very special place in my heart.

But there's zillions of great moments, in my opinion more good ones than bad ones, although admittedly the last two seasons were rather disappointing IMO (but the show is still in a better state than the Simpsons currently are). Oh yeah, also I love the "they took our joooobs" running gag. Makes me lol every single time.
Haha, I actually thought of mentioning that one. I particularly loved that they displayed "Emmy award winning show" (or something like that) during the most moronic and disgusting moments of that episode.

Edit: Oh yeah, I think I found one the biggest lows: The "Make Love, Not Warcraft" episode. I mean, it was very original and funny but I think it was still simply wrong in many ways starting with the fact that the episode felt more like an ad for WoW than like legitimate satire. The amount of respect for WoW and Blizzard they showed in that episode did not at all fit the overall style of the show.

Good and great:

Black Friday Trilogy- especially the comment about pre-orders and the "Brack Friday Bunduru" especially since that comment about pre-ordering was so true:
https://www.youtube.com/watch?v=GJpwUTMwiVY

Crack Baby Basketball

Christmas Critters

Imagination Land trilogy

Humancentipad


Dislikes and disappointments:

World War Zimmerman- a lot of great potential wasted and the jokes were repetitive in a bad way

Faith Hill (spelling?)- the entire episode revolved around the same unfunny joke. One of the risks of making an episode that revolves around just one joke is that if the joke sucks, the whole episode collapses