Marvin: "I am at a rough estimate thirty billion times more intelligent than you. Let me give you an example. Think of a number, any number."
Zem: "Er, five."
Marvin: "Wrong. You see?"

"My capacity for happiness," he added, "you could fit into a matchbox without taking out the matches first"

Arthur: "Marvin, any ideas?"
Marvin: "I have a million ideas. They all point to certain death."

"What's up?" [asked Ford.]
"I don't know," said Marvin, "I've never been there."

I could calculate your chance of survival, but you won't like it.

"I've seen it. It's rubbish." About a Magrathean sunset that Arthur finds magnificent.

"I'd give you advice, but you wouldn't listen. No one ever does."

"Not that anyone cares what I say, but the Restaurant is on the other end of the universe"

"[Trillian] is one of the least benightedly unintelligent life forms it has been my profound lack of pleasure not to be able to avoid meeting."

"Here I am, brain the size of a planet and they ask me to take you down to the bridge. Call that job satisfaction? 'Cos I don't."

"Pardon me for breathing, which I never do anyway so I don't know why I bother to say it, oh God, I'm so depressed. Here's another one of those self-satisfied doors. Life! Don't talk to me about life."

"This Arthur Dent," comes the cry from the farthest reaches of the galaxy, and has even now been found inscribed on a deep space probe thought to originate from an alien galaxy at a distance too hideous to contemplate, "what is he, man or mouse? Is he interested in nothing more than tea and the wider issues of life? Has he no spirit? Has he no passion? Does he not, to put it in a nutshell, fuck?"
Those who wish to know should read on. Others may wish to skip on to the last chapter which is a good bit and has Marvin in it.