*sigh* So many good ones
(this is probably misquoted but you get the idea)
Lisa and Homer see a news report of an oil spill on tv, showing lots of animals covered in oil
Lisa: Oh no!
Homer: Oh, don't worry sweetie. There's plenty more oil where that came from.
Disco Stu is good as well (in my sig) and Duff Man is always good for a laugh. Dammit, every character has had funny lines over the course of the series!