'Don Quixote' - the first novel (arguably) and also (arguably) the best: but it's not a 'quick read'.
To suggest 'The Catcher in the Rye' (as mentioned by other answerers) and 'To Kill a Mockingbird' may be clichéd, but a cliché doesn't become a cliché without more than a grain of truth in the first place.
My conversation, and life, wouldn't be the same if I hadn't read - in no particular order - 'Treasure Island', 'Gulliver's Travels', 'Black Beauty', 'Vanity Fair', 'Lolita', 'The Big Sleep', 'The Gulag Archipelago' and 'American Psycho' ... to name but a few.
Having said that, I'm going away next week and have the latest books by Karin Slaughter and Jeffrey Deaver packed ...