Do you want a line that is:
* Most recognizable by everyone? "Hakuna Matata" from *The Lion King* is a strong contender.
* Most inspiring? "If you can dream it, you can do it" from *The Sorcerer's Apprentice* segment of *Fantasia* is a classic.
* Most funny? "I'm not bad, I'm just drawn that way" from *The Little Mermaid* is a good one.
* Most sentimental? "You are braver than you believe, stronger than you seem, and smarter than you think." from *Winnie the Pooh* is a heart-warmer.
To help me give you a better answer, could you tell me what kind of famous line you're looking for?