For me, there's really no topping "King-Size Homer". Homer despises the nuclear plant's new exercise program, and decides to gain 61 pounds in order to claim a disability and work at home. He soon begins to experience the negative aspects of being obese, and his life starts falling apart. It's amazing, and there's rarely a day that I honest-to-God quote something from it. Whether it's Homer's dialogue with the computer ("To start press any key. There doesn't seem to be any "Any Key"! I see Esc, C-tar-l and Pig Up.") to Bart's assertion that in the future he'll "wash himself with a rag on a stick" to Lisa's defence and subsequent embarrassment of defending Homer to Ralph Wiggum on the school bus after Homer drives next to it with a stolen ice cream truck ("Mmm, that's raspberry!"). It's just an amazing piece of The Simpsons and of television in general.
And yes, I am Simpsons crazy! As long as Simpsons is defined as (1989-1998)