Fahrenheit 451 is a relatively short book, so reading it will give a sense of the most important quotations. For sources online, check Google Books for an eBook preview, as well as Amazon.com. Also, read the eNotes study guides available on this website for context-sensitive quotations.
One important quote comes early, when Montag is burning a building:
With his symbolic helmet numbered 451 on his stolid head, and his eyes all orange flame with the thought of what came next, he flicked the igniter and the house jumped up in a gorging fire...
This quote establishes Montag as a "fireman," but not the sort that modern society understands. Montag sets fires instead of fighting them; he burns books because they are illegal, and he burns people if they won't surrender. The "fireman" in this world is a cruel parody of the real firemen who serve humanity in the real world.
Another important quote comes when Montag and his fellow firemen are responding to a call about an old woman who is keeping books:
The woman knelt among the books, touching the drenched leather and cardboard, reading the gilt titles with her fingers while her eyes accused Montag.
"You can't ever have my books," she said.
(Bradbury, Fahrenheit 451, Google Books)
This quote shows both the inhumanity of Montag's actions -- he is destroying a person's beloved possessions without cause -- and the fierce love of books and reading that will soon possess Montag himself. The old woman refuses to leave her kerosene-soaked house, instead lighting herself and the house on fire rather than allowing the firement to destroy it. The strength of her conviction stuns Montag, and he finds himself even more attracted to the forbidden knowledge contained in books.