Oh so many! When I was younger I really liked those royal diaries (each book is a diary of a famous princess), because I've always been into historical fiction.
Other faves have to be the Arthur series by Kevin Crossley Holland (The Seeing Stone, At the Crossing-Places and King of the Middle March). Philip Pullman said he was spellbound by these books. I'd have to agree.
His Dark Material books were also excellent.
But I'd have to say the silverwing books by Kenneth Opple (Silverwing, Sunwing and Firewing). They are so excellent. Read them people, read them. I don't care if you like fantasy, horror, whatever. YOU'LL LOVE THEM!!!!!!!!!! They are some of my favourite books of all time. I've read them over and over. The first one is the best, but the other two are still really good. I cannot praise them enough!!! If I can just get one of you to read them I'll be so happy, cuz you'll enjoy them!!!!! They're that good.
Honorable mention to The Emily of New Moon books and The Anne of Green Gable books. I haven't read them for years, but they were good.