Outlander by Diana Gabaldon
To get a couple of things out of the way, first if you've read the book, no my Claire wasn't named for the Claire in the book. I liked the name long before I read this book, but the association didn't hurt. Second, if you go to Amazon and start reading the info on the book, one of the first descriptions of this book you will see is "600-page time-travel romance". Don't be put off by this!
Yes, the book is long. Yes, there is a little time travel, but more than anything I hate this book being described as a romance. I don't read romances. To me those are the bodice rippers with Fabio on the cover.
Outlander is different. There is romance, there is sex, but the context is different from other "romance" books. In Outlander it's all within an ACTUAL relationship. Romance, sex, arguments, laughter. All of the things that we all experience in our relationships.
In addition to being set in the fabulous Scottish countryside, Outlander is meticulously researched. There are so many layers to this book that it really doesn't get old, even after many readings. And, if you prefer audio books to print versions, the UNABRIDGED audio read by Davina Porter is amazing!