I suppose Harry Potter. I did recently find a 3 volume for the lord of the rings,but sometimes I prefer movies over books. I do like stephen king stories,but have not tried any of his series.
Actually, none of that genre. I really do not like fantasy books. Not at all. I love reading, though. Can't find enough to read in my small town. I like Nevada Barr's books that revolve around one character's adventures, park ranger Anna Pigeon, so I guess that qualifies as a series.
I own and have read all of the books in the poll. They are all good in their own way, but there are so much better ones out there. If I had to choose, Chronicles of Narnia are the best, because of the message behind them. I agree with another poster, Vampire Academy is great and so are the House of Night books. Also, the Percy Jackson books were good. (OK, I don't honestly think I have disliked a book other than Johnathon Norell and Mr. Strange, I couldn't get into it.) For any of you adults who have read Twilight, read The Host by Stephenie Meyer. It is totally different, but good and geared towards adults.