Mine is, without doubt, the one where Cartman draws a face on his hand and says it's Jennifer Lopez. Some classic lines in that:

"There. That's three more songs we've written already! Your style of music is so easy it doesn't require any thought at all!"

...and the general silliness of it makes me cry laugh ("baby lets make a run for the border, i got a hunger only tacos can't stop, i know exactly what i'll order, three tacos, two coscodas and a soda pop"

So, what are YOUR favourite episodes?