For what little it's worth, I aired my personal opinions on several of the books under discussion just a few weeks ago here: cs.finescale.com/.../1605250.aspx .
I've sung the praises of George Campbell's Neophyte Shipmodeler's Jackstay several times in the Forum. If I could recommend one book to a newcomer to sailing ship modeling, this would be it. Yes, it's aimed at solid-hull wood kit modelers. (It was originally published as sort of a general-purpose instruction book for Model Shipways kits.) And it's long in the tooth. (It was published, if I remember right, in about 1960.) But it contains all sorts of solid modeling advice (the techniques of rigging plastic and wood models aren't much different), and, given its brevity, a vast amount of information about the history of sailing ship technology. A person who learned everything in that book would be well on the way to being really knowledgeable about the subject.
I share Schoonerbumm's enthusiasm for the Harland book. So far as I know, there's nothing quite like it. I have the impression that it's currently out of print, but used copies should be available on the web.
I can recommend Mondfeld's book with a couple of reservations. First, it's very, very European in its focus. (Some of the references to wood types and fittings, for instance, won't be as relevant to American modelers.) Second, it covers so much ground that it can't cover any subject with much thoroughness. But as a start for a library on ship modeling it's hard to beat.
Harold Underhill's books are superb. But bear in mind that they refer almost exclusively to one sort of ship: late-nineteenth- and early-twentieth-century merchant vessels. If you're building a model of the Cutty Sark, the Archibald Russell, or the Pamir, Underhill's Deep Water Sail and Masting and Rigging: The Clipper Ship and Ocean Carrier should be on your must-read list. But if you're building an eighteenth-century frigate those books will be almost completely irrelevant.
Lever's Young Officer's Sheet Anchor is a primary source (not a modeling book) on warship and merchant ship rigging in the very late eighteenth and early nineteenth centuries. It's extremely valuable for learning prototype practice in that period (but useless for Spanish galleons or twentieth-century merchantmen). I particularly recommend the edition published by, of all people, Lee Valley Toolworks: http://www.leevalley.com/US/wood/page.aspx?p=40983&cat=1,46096,46117&ap=1 . This edition contains updates by another author that bring the book up to the 1850s. It's a nice, hardbound volume, and it doesn't cost much.
Unfortunately there's a dearth of books (and articles) dealing with plastic sailing ships. A big part of the problem is that the potential market is so small. Another is that so many people who are interested in sailng ship models turn their noses up (wrongly, in my opinion) at anything that isn't made of wood. Yet another - common to ship modeling books in general - is that books aimed at beginners tend to be written by people who never got far beyond beginner status themselves, and, to put it bluntly, don't really know what they're talking about. (See Roth, Milton, above.) The experts usually write books that demonstrate their expertise and experience. (Exception: see Campbell, George, above.) Donald McNarry is one of my favorites - but when I look at his models I feel like giving up. The same goes for modelers like C. Nepean Longridge and Phillip Reed - superb, inspiring stuff, but far beyond the reach of a newcomer.
Moving away from modeling books, the history of ships is, of course, a vast subject on which literally thousands of books have been written. If you're interested in learning about it, I think my best advice would be to make up your mind about a particular period that interests you and do another post; I'm sure lots of Forum members would make good suggestions. If I had to make one suggestion for somebody starting a library on the subject (and a library is what you'll end up with, if you keep at it), it would be the twelve-volume Conway's History of the Ship series. It's out of print now (I think), and it never was cheap. But your local public or university library may have a set, and used copies should should be available on the web. For a while the series was available in paperback; if you can find a used paperback copy the price shouldn't be too awful. (If you're interested in Napoleonic-period warships, for instance, the volume you want is The Line of Battle: The Sailing Warship From About 1640 to the Introdution of Steam c. 1840.) First-rate books that feature the latest scholarly thinking (as of the 1990s), along with lots of illustrations and an excellent, up-to-date bibliography.
Anybody who's been in the hobby for a while good go on all day about this topic. Hope this helps a little. Good luck; it's a great hobby.
Update an hour later: I just checked a couple of bookstore websites (Amazon and Barnes and Noble). It seems that used copies of the Conway's History of the Ship volumes can be found all right (the series is indeed out of print), but the prices are pretty hideous. The cheapest copy of Cogs, Caravels, and Galleons listed was about $75.00, and the most expensive was (believe it or not) $9,999.00. All the copies listed were hardbound. If all twelve volumes are going for the same prices, a full set would cost...well, let's not talk about it.
The height of ridiculousness, though, has to be this: http://www.amazon.com/gp/offer-listing/B008T1VONE/ref=dp_olp_used?ie=UTF8&condition=used . For the record, in the unlikely event that some insane person buys it, I won't make a nickel.
Well, libraries are wonderful places....