Just one of them? I have quite a few that I happily re-read again and again.
All the Sharon Penman books (new one just out on Richard I, which I must read at some point). Anne of Green Gables series gets re-read at least once a year. Also 'Blue Castle' and the 'Emily Series' by LM Montgomery too.
Narnia Chronicles (not quite as often), Jane Eyre and Pride and Predjudice.
Day 6 - A book you can only read once (no matter you love or hate it)
Day 7 - Book that reminds you of someone
Day 8 - Book that reminds you of a certain place
Day 9 - The first book you ever read
Day 10 - Book from your favourite author
Day 11 - Book you once loved and now hate
Day 12 - Book that a friend recommended
Day 13 - Book that makes you laugh
Day 14 - Book from your childhood
Day 15 - 4th book from the left on your shelf
Day 16 - 9th book from the right on your shelf
Day 17 - Close your eyes and get any book from your shelf
Day 18 - Book with the most beautiful cover
Day 19 - Book that you never wanted to read
Day 20 - Book that you read at school
Day 21 - Most stupid book you read at school
Day 22 - Book on your shelf with the most pages
Day 23 - Book on your shelf with the least pages
Day 24 - Book that nobody would expect you read/loved it
Day 25 - A book where the main character is almost like you
Day 26 - Book you would read to your children
Day 27 - A book where the main character is your idol
Day 28 - Thank God this book was made into a movie
Day 29 - Darn, why did they make this book into a movie?
Day 30 - First erotic book you ever read
Day 31 - Book series you are collecting