Some good ones found on wikki quote.
# "Far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the Galaxy lies a small, unregarded yellow sun. Orbiting this at a distance of roughly ninety-eight million miles is an utterly insignificant little blue-green planet whose ape-descended life forms are so amazingly primitive that they still think digital watches are a pretty neat idea."
* The Hitchhiker's Guide to the Galaxy p1
* This is the first line of the novel.
# "Humans are not proud of their ancestors, and rarely invite them round to dinner."
# "In those days spirits were brave, the stakes were high, men were real men, women were real women and small furry creatures from Alpha Centauri were real small furry creatures from Alpha Centauri."
* The Hitchhiker's Guide to the Galaxy p114
# "In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move."
# "There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable... There is another theory which states that this has already happened."
# "The Hitchhiker's Guide to the Galaxy has a few things to say on the subject of towels.
A towel, it says, is about the most massively useful thing an interstellar hitchhiker can have. Partly it has great practical value— you can wrap it around you for warmth as you bound across the cold moons of Jaglan Beta; you can lie on it on the brilliant marble-sanded beaches of Santraginus V, inhaling the heady sea vapours; you can sleep under it beneath the stars which shine so redly on the desert world of Kakrafoon; use it to sail a mini raft down the slow heavy river Moth; wet it for use in hand-to-hand combat; wrap it round your head to ward off noxious fumes or to avoid the gaze of the Ravenous Bugblatter Beast of Traal (a mindboggingly stupid animal, it assumes that if you can't see it, it can't see you—daft as a bush, but very ravenous); you can wave your towel in emergencies as a distress signal, and of course dry yourself off with it if it still seems to be clean enough.
More importantly, a towel has immense psychological value. For some reason, if a strag (strag: non-hitch hiker) discovers that a hitch hiker has his towel with him, he will automatically assume that he is also in possession of a toothbrush, face flannel, soap, tin of biscuits, flask, compass, map, ball of string, gnat spray, wet weather gear, space suit etc., etc. Furthermore, the strag will then happily lend the hitch hiker any of these or a dozen other items that the hitch hiker might accidentally have "lost". What the strag will think is that any man who can hitch the length and breadth of the galaxy, rough it, slum it, struggle against terrible odds, win through, and still knows where his towel is is clearly a man to be reckoned with."
# "Hence, a phrase that has passed into hitchhiking slang, as in, 'Hey you sass that hoopy Ford Prefect? There's one frood who really knows where his towel is.'
(sass: know, be aware of, meet, have sex with; hoopy: really together guy; frood: really amazingly together guy)"
# "Anyone who is capable of getting themselves made President should on no account be allowed to do the job."
# "He hoped and prayed that there wasn't an afterlife. Then he realized there was a contradiction involved here and merely hoped that there wasn't an afterlife."
# "There is a moment in every dawn when light floats, there is the possibility of magic. Creation holds its breath."
# "The ships hung in the sky in much the same way that bricks don't."
* The Hitchhiker's Guide to the Galaxy p34
# "...and you will enter the long dark teatime of the soul."
# "The thing he realized about the windows was this: because they had been converted into openable windows after they had first been designed to be impregnable, they were, in fact, much less secure than if they had been designed as openable windows in the first place."
# "The last time anybody made a list of the top hundred character attributes of New Yorkers, common sense snuck in at number 79."
# "A common mistake that people make when trying to design something completely foolproof was to underestimate the ingenuity of complete fools."
# "He felt that his whole life was some kind of dream and he sometimes wondered whose it was and whether they were enjoying it."
* The Hitchhiker's Guide to the Galaxy p19
# "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair."
* Mostly Harmless
# "It is a mistake to think you can solve any major problems just with potatoes."
* Life, the Universe and Everything, chapter 24
# "On the planet earth, man had always assumed that he was more intelligent than dolphins because he had achieved so much—the wheel, New York, wars and so on—while all the dolphins had ever done was muck about in water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man—for precisely the same reasons."
* The Hitchhiker's Guide to the Galaxy p156
# "Curiously enough, the dolphins had long known of the impending destruction of the planet Earth and had made many attempts to alert mankind to the danger; but most of their communications were misinterpreted as amusing attempts to punch footballs or whistle for tidbits, so they eventually gave up and left the Earth by their own means shortly before the Vogons arrived."
* The Hitchhiker's Guide to the Galaxy p156
# "It is known that there is an infinite number of worlds, simply because there is an infinite amount of space for them to be in. However, not every one of them is inhabited. Therefore, there must be a finite number of inhabited worlds. Any finite number divided by infinity is as near to nothing as makes no odds, so the average population of all the planets in the universe can be said to be zero. From this it follows that the population of the universe is also zero, and that any people you may meet from time to time are merely the product of a deranged imagination."
# The problem is, or rather one of the problems, for there are many, a sizable number of which are continually clogging up the civil, commercial, and criminal courts in all areas of the Galaxy, and especially, where possible, the more corrupt ones, this. The previous sentence makes sense. That is not the problem. This is: Change. Read it through again and you'll get it.
# The history of every major galactic civilization has passed through three distinct and recognisable phases: those of survival, inquiry, and sophistication. Otherwise known as the ‘How’, ‘Why’, and ‘Where’ phases. For instance, the first phase is characterised by the question: “How can we eat?” The second by the question: “Why do we eat?” And the third by the question: “Where should we have lunch?” The history of warfare is similarly subdivided though here the phases are retribution, anticipation, and diplomacy. Thus, retribution: “I’m going to kill you because you killed my brother.” Anticipation: “I’m going to kill you because I killed your brother.” And diplomacy: “I’m going to kill my brother and then kill you on the pretext that your brother did it.” Meanwhile, the Earthman Arthur Dent, to whom all this can be of only academic interest, as his only brother was long ago nibbled to death by an okapi, is about to be plunged into a real intergalactic war.
* Radio series, Fit the Sixth.
# The designer of the gun had clearly not been instructed to beat around the bush. "Make it evil," he'd been told. "Make it totally clear that this gun has a right end and a wrong end. Make it totally clear to anyone standing at the wrong end that things are going badly for them. If that means sticking all sort of spikes and prongs and blackened bits all over it then so be it. This is not a gun for hanging over the fireplace or sticking in the umbrella stand, it is a gun for going out and making people miserable with."
* The Restaurant At the End of the Universe pg 262-263
