Oh god, there's so many amazing quotes in this series. When I read the question, though, the first to pop into my head was, "A sword wields no strength unless the hand that holds it has courage," from the Hero's Shade in Twilight Princess. I dunno, it's just a really cool quote and I love it, and I love Hero's Shade. Especially how he says something like, "The Back Slice! Let it be hewn into your mind!" Lol. Hewn.
All of Sheik's quotes are great. The classic, "It's dangerous to go alone! Take this," is always a great one.
Not to mention everyone's favorite, "Hey! Listen!"