There are wayyy too many, but here's my top 10, in no particular order:
Homer: From now on, there are three ways to do things: the right way, the wrong way, and the Max Power way.
Bart: Isn't that just the wrong way?
Homer: Yeah, but faster!
Lionel Hutz: Well, he's kind of had it in for me ever since I accidentally ran over his dog. Actually, replace "accidentally" with "repeatedly," and replace "dog" with "son."
Ralph: Hi, Super Nintendo Chalmers!
[Santa's Little Helper goes off running with George Bush, leaving Homer all alone]
Homer: I guess you might say he's barking up the wrong Bush.
Homer's Brain: There it is, Homer. The cleverest thing you'll ever say and nobody heard it.
Lisa: Dad, don't you think you're overreacting?
Homer: Don't you think you're *under*reacting?
Lisa: This conversation is over.
Homer: This conversation is *under*.
Marge: [on radio] Husband on murderous rampage. Send help. Over.
Chief Wiggum: Whew, thank God that's over. I was worried for a little bit.
Homer: I think I'll make myself Vice President. No wait- JUNIOR Vice President.
Lisa: Do we have any food that wasn't brutally slaughtered?
Homer: Well, I think the veal died of loneliness.
(Homer is yelling at Bart for shoplifting)
Homer: How could you?! Haven't you learned anything from that guy who gives those sermons at church? Captain Whatshisname? We live in a society of laws! Why do you think I took you to all those Police Academy movies? For fun? Well, I didn't hear anybody laughing, did you? Except at that guy who made sound effects. *Makes sound effects and laughs.* Where was I? Oh yeah! Stay out of my booze!
Sideshow Bob: Attempted murder, now honestly, what is that? Do they give a Nobel Prize for attempted chemistry?