Hi Lisa - I've been in a book group since 1995, so we have read over a hundred books. I do try to keep some ratings of the books we read, but I'm not always up to date. And not all the books we've read have been rated. But according to my records, here are some of our favorites - based on how much we enjoyed reading them and how discussable they were (not necessarily in any order):

A Prayer for Owen Meany - John Irving
Bean Trees - Barbara Kingsolver
A Thousand Acres - Jane Smiley
Cold Mountain - Charles Frazier
Handmaid's Tale - Margaret Atwood
A Yellow Raft in Blue Water - Michael Dorris
The Girls - Lori Lansens
Snow Flower and the Secret Fan - Lisa See
Snow Falling on Cedars - David Guterson
Water for Elephants - Sara Gruen
Sarah's Key - Tatiana de Rosnay
People of the Book - Geraldine Brooks

Some that haven't been rated but were group favorites were:

Angle of Repose - Wallace Stegner
Because of Winn Dixie - Kate DiCamillo (a YA book)
Olive Kitteridge - Elizabeth Strout
The Namesake - Jhumpa Lahiri
Peace Like a River - Leif Enger
To Kill a Mockingbird - Harper Lee

Also, The Help, by Kathryn Stockett, received a perfect 5 out of 5 from all of those who read it.

Much of this is pretty standard book club fare, which is what my book group seems to prefer. The above books were not necessarily my favorites, although I agreed with many of the ratings. If I were to list my faves, they would be (not in any order):

Sarah Canary - Karen Joy Fowler (Surprise!)
Cider House Rules - John Irving
East of Eden - Steinbeck
Smilla's Sense of Snow - Peter Hoeg
Motherless Brooklyn - Jonathan Lethem
House of Sand and Fog - Andre Dubus
Montana 1948 - Larry Watson
Life of Pi - Yann Martel (close to the top of my list)

Each book group has it's own personality, just as individuals do. Over time, you will discover you group's personality and will learn the types of books that work and the type that don't work.

Good luck ... and happy reading and discussing.

I agree with Sarah-our book club has been in business for 10 years, and one reason I think we have successfully continued is that we do not work off an artificial list. Instead, we take turns bringing three or four choices to a meeting, the group chooses and the "bringer" leads the next discussion. We do have a couple group-specific rules: book length, no science fiction, and no more Jodi Pichoult after we read 4 in two years and a couple of us rebelled!
Books that have resulted in great discussions:

The Prime of Miss Jean Brodie
The People of the Book
The Book Thief
Snow Flower and the Secret Fan
The Dress Lodger
The Razor's Edge
The Painted Veil
A Thousand Splendid Suns
Fall On Your Knees (several of us hated this book, but it was a good discussion!)
The Tattooed Girl
The Girl With the Dragon Tattoo
Alas, Babylon
A Thread of Grace

I forgot to mention how we pick our books. In December we have a holiday party. We each bring a wrapped book (that we have already read and liked) and we have an exchange. We pick numbers and go in order. The person who gets number 1 gets to pick the first gift/book and then at the end gets to decide whether or not to steal someone else's pick. The others get to steal books throughout the exchange. For example, if your number is five and you like the book that number three chose, you can steal it. But you have to do it before you open any of the wrapped books. Books can only change hands three times - just in case there's a really popular book that year. We also have one person that everyone contacts to give her the name of the book they will be bringing, just to be sure we don't get duplicates.

We then each read the book we received and at our January meeting we decide which books to put on the list for that year. This way, at least two of us have read and liked each choice. At least that's the way it's supposed to work.