I second The Mitford Series. You will fall in love with the characters.
I also love Alexander Whitehall Smith - The #1 Ladies Detective Agency series. It's a hoot! I have the first of his new series loaded on my Kindle, but haven't started it yet.
Very lightweight, fun reads - the Sister Chicks series.
I also love anything by Margaret Truman - mysteries set in and around the Washington DC area.
In the mystery genre - I also have read just about every Agatha Christie novel published - several times over!
Dan Brown's books are engrossing - but if you've seen the movies, for me that can be a distraction. I liked reading Angels and Demons - after I had been to Rome and seen some of the places he mentioned in the books. Same with the Da Vinci Code - it was fun seeing the Louve after reading his book. My sister and I went on a "hunt" so to speak for the paintings he mentions in it :)
Oh - another book I really enjoyed was Under the Tuscan Sun. I saw the movie also, but REALLY liked the book, especially since it has 3 or 4 chapters that are actually COOKBOOKS :) I really want to go back to Italy and to the town that is the setting for the book.