The main site contains details of many books with some relevance to Hertfordshire, including many out of print. If you want to know more about any book mentioned on this site and the relevant page does not give enough detail why not ask. Jon recently asked about Brig-General H. Page Croft's book "Twenty Two Months under Fire" and I have responded:
This book concentrates of descriptions of the battles and battlefields on the Western Front where the Herts Regiment was based, and a quick scan failed to reveal any named person from Hertfordshire and the only named place I spotted was to the training camp at Ashridge, where they were based on the day war was declared. This means that the book is of little relevance to anyone looking for specific references to individual soldiers, or what was happening in Hertfordshire at the time.
Remember that even if a book does not mention your ancestor it can contain much relevant background information about the place he lived in and the social circumstances which would have influenced his everyday life. And if you want to know more about a book before borrowing it from a library, or buying a copy, why not ask me about it.