Ooh, i'm going to have fun with this. I have a collection of quotes that I post on my blog. Looking up the authors may be tricky though.
Unfortunately i've amended some of them, so I can't really post those ones.
Unfortunately this first one is an actual quote, so it's not really from a Visual Novel (though it features in Sharin no Kuni, Himawari no Shoujo):
"The final test of a leader is that he leaves behind in other men the conviction and the will to carry on."
Walter Lippman
"No matter how important a person is, some day you will lose them. No matter how much you desire it, eternity is one thing you will never possess. It's the time you do spend with that person that's important, so that you can meet your parting without regret."
Yuko Amamiya, Ef - A Fairy Tale of the Two
"They're called miracles because they don't happen."
"They're called miracles because they do happen, even when things seem hopeless".
Unfortunately I can't remember the characters for this one, though the VN is Kanon.
"It's better to be alone in a desolate place than it is to be alone in a place with many people."
Chihiro Shindou, Ef - A Fairy Tale of the Two
"Samurai die for their own sake. Knights die for the sake of another. That is why I have always called myself a knight."
Sakuya Ohtori, Rewrite
"Rules are not made to bind you, they exist so that you may know your freedoms."
Not sure on character, but the video game is Nier.
"The only thing waiting for you after giving up is regret."
You Kogasaka, Hoshizora no Memoria