Another great thing about this episode is one of my favorite characters is featured prominently in it: The Crazy Cat Lady!!!
<3 <3 My Hero <3 <3
Personally, all of my favorite Simpsons Episodes have a psychedelic animation sequence. Here are some links to others:
Weekend At Burnsies
Homer is prescribed medical marijuana after sustaining serious eye injuries from a once friendly flock of crows
El Viaje Misterioso de Nuestro Jomer
Homer eats mexican chili peppers which make him trip balls. He then goes on a spiritual journey through a metaphorical desert with a fox (whose voice is Johnny Cash) as a spirit guide.