I can't pick just one so I'm going to pick some of the more unusual books that I like.
Liars and Saints and A Family Daughter, both by Maile Meloy.
Both about the Santerre family, but not exactly the same, and I can't say why they are unusual without giving away too much. If I had written a book I would have liked to have written Liars and Saints.
Important Artifacts and Personal Property from the Collection of Lenore Doolan and Harold Morris, Including Books, Street Fashion, and Jewellery by Leanne Shapton. It's unusual because it's set like an auction catalogue, auctioning items collected during a four year relationship and being sold now the couple have split up.
Happenstance by Carol Shields. It is like two books in one really, one half tells the Wife's Story and the other half tells the Husband's Story. You read to the middle and then flip the book over and read to the middle from the other side. It doesn't mater which story you read first. I miss Carol Shields writing now, I hope she's not forgotten since her death. Her books are very good, very thoughtful.
Desperation and The Regulators, both by Stephen King. They tell two very different stories but using the same characters. In Desperation, a group of people are trapped in the Nevada desert with a supernatural entity. In The Regulators, the same people are trapped on a residential street as a supernatural event happens. The books are stand alone books and in both it's only that one event that has happened. There's no "can you believe this is happening to us again" because it isn't, in both books it's the one and only time. People who die in one book survive in the other.