A fairly recent one, courtesy of Nelson Muntz, after he jumps out the back of the school bus:
“Bullies rule!”
In the “outsider art” episode, Homer comes across a Matt Groening artwork at the museum (a picture of a Life in Hell character, I vaguely recall) and makes a disparaging remark, whereupon he is attacked by a giant eraser (which turns out to be two workmen carrying a Claes Oldenburg sculpture shaped like a giant pencil).
Hi, SDMB, longtime listener, first time caller, love your show.
From a clips show I saw the other day, I believe it was “Gump Roast”.
At the end is a still shot of a water-skiing Homer, jumping over a shark…
And while we’re on the subject of The Simpsons, my favorite line from any episode ever is from the Homer talks to god and skips church episode.
Homer is watching the 3 stooges on TV.
Homer: “Moe is their leader”
As with so many things, its just something about the way he said it. Come to think of it, that episode is one of my all time faves.
I always told myself I would save my debut SDMB post for something really important 
I love this episode too, but one of my all-time Simpsons favorite moments is when he talks to God. I love it Snowball II nuzzles God’s leg and He casually rubs his head with one massive finger. It’s what I imagine a loving God would do.