An excellent book that crosses the sci-fi/ mainstream line is The Time Traveler’s Wife by Audrey Niffenegger. Henry, a man with a strange disorder that forces him back and forth in time finds himself regularly coming to the same field and the same girl, Clare. Clare eventually grows up and falls in love with Henry. This book makes quite a brain workout as you have to bend your mind around the idea of time—Henry first meets Clare when he twenty eight and she is 20; Clare first meets Henry when he is thirty six and she is six. But as much as this book focuses on time, the central theme is the love between Henry and Clare. No matter when Henry is, his life focuses on making Clare happy and Clare in turn would go months without seeing Henry but always keep him in her thoughts. It is both moving and tragic—expect tears. Oh, and the movie is apparently coming out in December starring Rachel McAdams and Eric Bana.