I have far more than ten favorites, so here is just a sampling, in no particular order:
1. "Remember that at any given moment there are a thousand things you can love." - The Realm of Possibility by David Levithan
2. "Strange as it may seem, I still hope for the best, even though the best, like an interesting piece of mail, so rarely arrives, and even when it does it can be lost so easily." - The Beatrice Letters by Lemony Snicket
3. "Imagine 4 years.
Four years, two suicides, one death, one rape, two pregnancies (one abortion), three overdoses, countless drunken antics, pantsings, spilled food, theft, fights, broken limbs, turf wars–every day, a turf war–six months until graduation and no one gets a medal when they get out. But everything you do here counts.
High school." - Cracked Up to Be by Courtney Summers
4. "Thomas Edison's last words were 'It's very beautiful over there'. I don't know where there is, but I believe it's somewhere, and I hope it's beautiful." - Looking for Alaska by John Green
5. "Instead, I try to adjust to the dawn, letting the tears fall where they may, because it is morning; it is morning, and there is so much to see." - The Sweet Far Thing by Libba Bray
6. "There are certain people who come into your life, and leave a mark. . . Their place in your heart is tender; a bruise of longing, a pulse of unfinished business. Just hearing their names pushes and pulls at you in a hundred ways, and when you try to define those hundred ways, describe them even to yourself, words are useless." - Sweethearts by Sara Zarr
7. "With her foot on the threshold she waited a moment longer in a scene which was vanishing even as she looked, and then, as she moved and took Minta’s arm and left the room, it changed, it shaped itself differently; it had become, she knew, giving one last look at it over her shoulder, already the past." - To the Lighthouse by Virginia Woolf
8. "Things that matter are not easy. Feelings of happiness are easy. Happiness is not. Flirting is easy. Love is not. Saying you’re friends is easy. Being friends is not." - Naomi and Ely's No Kiss List by David Levithan and Rachel Cohn
9. "Maybe a friend is someone who wants your updates. Even if they're boring. Or sad. Or annoyingly cutesy. A friend says "Sign me up for your boring crap, yes indeed"--because he likes you anyways. He'll tolerate your junk" - Real Live Boyfriends by E. Lockhart (It has been far too long since I've professed my love for Ruby Oliver.)
10. "For the two of us, home isn't a place. It is a person. And we are finally home." - Anna and the French Kiss by Stephanie Perkins