My favorite would have to be Marge vs. The Monorail. The infectious song, great guest appearances, Homer's classic enthusiasm that's not backed up by thought, his later heroics etc. The episode seemingly follows the format of "What if Homer did X?" but it is just so funny. Not to mention it is filled with great quotes.
Leonard Nimoy: A solar eclipse. The cosmic ballet... goes on.
Man: Does anyone want to switch seats?
Marge: Homer, there's a man here who thinks he can help you.
Homer: Batman?
Marge: No, he's a scientist.
Homer: Batman's a scientist.
Marge: It's NOT Batman!
Homer: Marge, I wanna be a monorail conductor.
Marge: Homer, no.
Homer: It's my lifelong dream!
Marge: Your lifelong dream was to run out onto the field during a baseball game, and you did it last year, remember?
[Points to a framed newspaper reading "IDIOT RUINS GAME - Springfield forfeits pennant"]
Mayor Quimby: All right, I'm in charge here.
Chief Wiggum: Oh, run along, Quimby. I think they're dedicating a phone booth somewhere.
Mayor Quimby: Watch it, you talking tub of donut batter.
Chief Wiggum: Hey, I got pictures of you, Quimby.
Mayor Quimby: You don't scare me, that could be anyone's ass.
Marge: I still thing we should have used the money to fix Main Street.
Homer: Well, you should have written a song like that guy.
Marge: And that was the only folly the people of Springfield ever took on... Except for the Popsicle stick skyscraper, and that 50 ft magnifying glass, and the escalator to nowhere.
And of course, "Mono... D'OH!"
Leonard Nimoy: A solar eclipse. The cosmic ballet... goes on.
Man: Does anyone want to switch seats?
Marge: Homer, there's a man here who thinks he can help you.
Homer: Batman?
Marge: No, he's a scientist.
Homer: Batman's a scientist.
Marge: It's NOT Batman!
Homer: Marge, I wanna be a monorail conductor.
Marge: Homer, no.
Homer: It's my lifelong dream!
Marge: Your lifelong dream was to run out onto the field during a baseball game, and you did it last year, remember?
[Points to a framed newspaper reading "IDIOT RUINS GAME - Springfield forfeits pennant"]
Mayor Quimby: All right, I'm in charge here.
Chief Wiggum: Oh, run along, Quimby. I think they're dedicating a phone booth somewhere.
Mayor Quimby: Watch it, you talking tub of donut batter.
Chief Wiggum: Hey, I got pictures of you, Quimby.
Mayor Quimby: You don't scare me, that could be anyone's ass.
Marge: I still thing we should have used the money to fix Main Street.
Homer: Well, you should have written a song like that guy.
Marge: And that was the only folly the people of Springfield ever took on... Except for the Popsicle stick skyscraper, and that 50 ft magnifying glass, and the escalator to nowhere.
And of course, "Mono... D'OH!"