My God, it's hard to decide. Warriors, the Inheritance Cycle, and the Dark is Rising. If you have never read any of these, I suggest you run to the bookstore to do so now.
The only book series I have started beginning to end and enjoyed it SO much was J. K. Rowling's, Harry Potter series. Best book serie's I have read, thus far. =]
The book series I have liked are Elric of Melniboné, Harry Potter, The Land of Elyon, Lord of the Rings, stuff written by Jhonen Vasquez, and the Wrinkle in Time series. If Goosebumps, Sherlock Holmes, stuff written by H. P. Lovecraft, and Encyclopedia Brown count, then those also.
@ Mattsimme...Finally another Wheel of Time fan! Awesome!
Anyway my favourite book series is hands down The Lord of The Rings, followed in a close second by The Wheel of Time, then probably Harry Potter
I looked through my book shelf and I found a old book series that I used to read when I was in grade school. It is called... A Series of Unfortunate Event's by Lemony Snicket. I'm going to re-read this series again. =]
My favorite book series of all time is definitely The Chronicles of Narnia! I really love every single one of those seven books, and my absolute favorite is The Voyage of the Dawn Treader! So yeah, I was really psyched about the film on the cinema a while back, I actually saw the film five times!