For a young adult/teen Meg Cabot's young adult books. She is the best author. Also best selling. She wrote tons of books including the Princess Diaries (Movies based on her books), Mediator (upcoming movie), 1-800-Missing (TV show based on her books), All-American Girl (up coming movie), Jinx, Airhead and more. She has adult books too, so you can grow with her.
If you want more info or any of the authors website's email me.
You should use the website, What Should I read Next. This website will make perfect suggestions based on what you have read.