One of my favorite books about the incarnation is The Incarnation in the Gospels  in the Reformed Expository Commentary series.   I highly recommend it as a collection of sermons that are very encouraging and edifying to read and think about this Christmas season.

If you're looking for it for a Christmas gift for someone and want to buy it locally, it may be available at the Christian bookstore, Johnson and Taylor in Danada Square in Wheaton.  They stock a number of quality books and I noticed a robust commentary section when I was there.