Hi Lisa - that is kind of a wide open topic. Most advanced collectors already have favorite books on particular coin types. They tend to follow the old addage "Buy the Book BEFORE the coin". So unfortunately most "serious" collectors already have the BOOK. In addition, many of the kinds of books you seem to want are kind of rare themselves and require a great deal of searching and money.
Since my area of specialization is Mexican, I can give you a brief tutorial for that type. You first need to know which Mexican coins he collects. There are Colonial Mexican cob coins. Colonial Milled coins - Columnarios and Portraits. War of Independence issues. Profile Eagle series. Early Republic. The empires of Iturbide and Maximilian. Later Republic. Republican Decimal issues. Mexican Revolutionary issues. Federal Issues and then Modern issues. Each type has specific references. Some are better than others and some series are not well documented yet. For example, in the Colonial Milled area - the Columnarios are well documented in Gilboy's "Milled Columnarios of Central and South America" but the Portrait coins are covered by only out of date and RARE books.
Most serious collectors of Mexican coins are FORCED by cost and sheer numbers to Specialize in some small sub-set of the entire issue. My focus are the Early Republic Cap and Ray issues (counterfeit varieties).
But, you might be able to interest him with a very narrow book that focuses on an interesting area of Mexican Numismatics that few people spend much time with. If I had to pick one single book for a collector I don't know, that I find personally fascinating it would be "Hookneck, El Aguila de Perfil" by Clyde Hubbard and Dave O'Harrow. It is a smallbook 223 pages (8x11) but it is one of the most interesting books on early Mexican coins that I have ever read. It has some great pictures and covers topics rarely seen in the average coin book. It describes how dies were made, how the coins were produced and even has a section on the edge designs used. It is also relatively inexpensive about $35 and it is still available. It is written in Spanish and English and was published in 1997. There is a small supplement that you should also purchase. I know one of the authors well and I contributed to the Supplement (one of my unique counterfeits appears in that section). But I get no kick back from sales - in case you are wondering.