Pope John Paul II's book Love and Responsibility is gaining popularity. Check it out at catholic book stores (I must say that Borders has a good selection of books written by Catholic writers), or order it online here at Ignatius Press' site. I am a Pauline Cooperator, so I'd recommend -- anytime of the day (yes, I am biased! :-)) -- ordering through or visiting the nearest Pauline Books and Media Center in your area. The sisters will welcome you and be able to answer any questions you may have.
The Ignatius Press link is great because it'll take you to pages of the book, so you can view and read some of the text.
Fr. Samuel Medley, solt, is heading up a discussion group based on the book at his parish in Corpus Christi. If you are not from that area, check out his video below to see how you can benefit from the discussion.
Thank you, Fr. Samuel Medley!