Naval and Military Press has just released a Special Great War Catalog with over 400 titles in this one publication. It provides a full range of Divisional Histories all at 50% off. There are numerous Regimental and Official Histories, contemporary memoirs and more.
Some of the databases sold can be found online at some of the commercial websites so be careful. But this is a goldmine for readers wanting to know that a particular book even exists, or for those wanting to fill in the gaps in their personal library, or wanting to know more about the regiment or division in which their ancestor served, or learn specifics about the battles in which they served or died.
If you have an interest in World War One do download a pdf of the catalog, linked here. One of the benefits of downloading the pdf, or opposed to getting the newsprint version of the catalog which I was also sent, is that you can search it for any regiment, division, battle or word which is very handy in this packed catalog.