What have you already read? I've been in a group for about 6 years now. What we have found works well is to take one of our meeting nights about every 6 to 8 months & go to B & N or another large bookstore and do some shopping together. They often have suggestions for book groups & will arrange a seating area for us.
I know what you mean about some "good" books to read not necessarily making good discussion. For instance, we all love Patricia Cornwell, but her books don't really make good discussion books.
Some of our favorites have been Divine Secrets of the YaYa Sisterhood by Rebecca Wells and Poisonwood Bible by Barbara Kingsolver. We try to read an occasional book by a local author - there is a really good one by Billie Letts called The Honk and Holler Opening Soon. We try to vary our topic/themes somewhat: historical, literary fiction, comedy, suspense; it keeps things from getting stale. In the beginning we tended to read a lot of the Oprah books, but have strayed from that because many of them had similar themes or tones. Very good books though.
I think I have a list somewhere of our books if you would like more.