Katherine by Anya Seton

The story of Katherine Swynford and her love affair with the Duke of Lancaster. Filled with honest longing and uplifting surrender.
Rebecca by Daphne du Maurier

This book is so beautifully written that the story could be terrible and no one would be the wiser. Not a typical romance but it illustrates the limits of love and devotion in a way that will tug at your heartstrings.
Green City in the Sun by Barbara Wood

Chronicles several generations of misguided love. Set in Kenya this epic will make you reevaluate all of your thoughts on real love.
The Thorn Birds by Colleen McCullough

Exploding with sexual tension and repressed passion, be prepared to cry every other page and promise yourself that you will never settle for anyone other than your true love.
The Ice People by Rene Barjavel

This is one of my favorite books of all time, I rarely lend it out because of my tremendous fear that I'll never get it back(it's out of print). The 1960s science fiction novel recalls an old world love, literally frozen in time. Beautifully written, racy, and utterly romantic.
Love Poems by Pablo Neruda

The Chilean Nobel Prize Winner defines the love poem. Truely.
Other notable reads:
Gone With the Wind by Margaret Mitchell, The Time Traveler's Wife by Audrey Niffenegger, and Witness to my Life: Letters from Jean Paul Sartre to Simone de Beauvoir.
If you have any suggestions, I'd love to hear!