Just discovered that an updated version of Nathaniel Branden's The Psychology of Romantic Love is being released on January 31, 2008. I have not seen a copy so I don't know how much has been changed. Here is the description from Amazon.
"Originally published in 1980, this updated edition of The Psychology of Romantic Love explores the nature of romantic love on many levels-the philosophical, the historical, the sociological, and the physiological. Nathaniel Branden explains why so many people say that romantic love is just not possible in today's world and-drawing on his experience with thousands of couples-finds that such love is still a possibility for anyone who understands its essence and is willing to accept its challenges."