A few years ago I met William Atherton and told him "This is going to sound weird, but Walter Peck of the EPA is my favorite character in Ghostbusters." In his droll baritone he replied: "That doesn't sound weird at all. In fact, it's the sanest thing I've heard all day."
But back on topic, some of my favorite quotes are:
"Yes, have some."
"Let's show this prehistoric b**** how we do things downtown. THROW IT!"
"If there's a steady paycheck in it, I'll believe anything you say."
"When the light is green the trap is clean."
"...and the flowers are still standing!"
"Tell him about the Twinkie."