In a way that's kind of hard to pick.  Some of the books that have a very good grounding and that I loved near the start of my practice I (and others) find rather "fluffy" these days, but there is no denying a lot of the basic information is still good.  There have been a lot of changes in pagan writings over the years. 

If I was going to pick authors, I'd have to pick Scott Cunningham and Raymond Buckland.  Some of Buckland's is rather path-specific, but the techniques work no matter which path you ultimately choose, and I've found in meetings with other pagans that a lot of covens who run beginner classes use "Buckland's Complete Book of Witchcraft" (aka Buckland's big blue book...lol) as their textbook.  He does teach one method, however, and doesn't really offer alternatives.  For example, someone else in another book....(very possibly Kerr Cuhulain's "Full Contact Magick" but I'm not positive....I would strongly recommend this book as well, though, it's one of my VERY favorites), mentions the teaching of calling on Watchtowers when casting a circle and makes you think about exactly what a watchtower is and asks, "are you in a place or situation where you need a watchtower specifically, or would you be better served by calling the element in general instead?"  Are you seeking protection, or do you want the energies of the elements to join in your working?  Watchtowers are protections that sit just on the outer edges of the circle instead of calling the elements to the inside of your circle, and you should think about what you really NEED instead of blindly using one method.  Buckland's just says, "do it like this" and gives the watchtowers version of a circle casting without mentioning there are other ways.

This is one of the reasons I find it harder to pick one beginner book.  So much of the information in Buckland's book is invaluable, but there are things in there like I mention above, and things that are left out that I find integral to my practice, that I've absorbed from others, like Silver Ravenwolf, for example.  I mainly am talking about her trilogy, "To Ride a Silver Broomstick", "To Stir a Magick Cauldron", and "To Light a Sacred Flame".  Admittedly, there are some rather "fluffy" aspects to her writings, and a lot of people complain about that, but there is also a lot of good information in there, and a lot of techniques that I still use today, as well as a lot of things I read in there that I later modified to suit myself better (which I find I do to most things from most books...I read them and say, "I like that, but I'd like it better like this!" and change it or personalize it slightly.)  I can't say anything about any of her other books, I only have those three.  I hesitate these days to recommend them mostly because they have such a rep for "fluffyness" anymore, but they were useful to me!

Scott Cunningham's books are to me more of the basic elements of spell-casting.  He has a number of books that I still use as reference books for herbalism and crystals, and explores the elements and their uses in magick.  He also has some about general practice, like his "Wicca for the Solitary Practicioner" and that kind of thing, which are also good, but I've found his specialty topics more useful personally.

Edain McCoy writes some very worthwhile books as well.  There are others that I'm sure are good, but aside from Christopher Penszak's "Inner Temple of Witchcraft" and "Outer Temple of Witchcraft" the vast majority of what else I have are specialty types, rather than "wicca 101" general books.  (Don't think I'm specifically NOT recommending his either, I just was way beyond wicca 101 by the time I got his and haven't read them closely enough to say they're great or not, I mostly skimmed them.)

I'd suggest getting two or three authors' beginner books to get a good grounding in the basic ritual forms, and perhaps something specific to a tradition the beginner feels drawn to if there is one to get a good rounded idea of the core of the practice, and then supplement with specialty books, like the reference type books like the Scott Cunningham books ("Cunningham's Encyclopedia of Magickal Herbs", "The Complete Book of Incense, Oils, and Brews", "Earth, Air, Fire, and Water", DJ Conway's "Crystal Enchantments") because they help you learn which plants, which stones, which elements, are best suited to which purposes.  I'd also strongly suggest something on divination, whether divination in general or on one type in particular that appeals to the learner already.

Later, there are others that explore ritual in more depth, like "The Elements of Ritual" by Deborah Lipp and "Coven Craft" and "Ritual Craft" by Amber K that can greatly enhance your practice and/or your understanding of all of the aspects of a ritual, but I think those are better appreciated once the beginner has a good general grounding.

Ok, you caught me talkative today, this somehow ended up way beyond "recommend a first book for a beginner"....lol.... 

Scott Cunningham's Wicca for the Solitary Practicioner, was one of the first books I picked up. To me, his writing is a little flat. And in some areas I didn't think he went into enough explaination. I also picked up Silver Ravenwolf's To Ride a Silver Broomstick, this was before I heard how "Fluffy" she is. That book is good for looking up candle colors, and things of that nature.  But my favorite books have been by Raven Grimassi and Christopher Penczak.  I really like The Inner Temple of Witchcraft by Penczak. By Grimassi, I've read and would definitely recommend Spirit of the Witch, this one is good for those who are completely new to the Pagan world and Witchcraft. I've even shared my copy with a couple of members of my family, so they will have a better understanding on witchcraft and Paganism/Wicca. Currently I'm reading The Witches' Craft by Grimassi, it goes further in to detail then Spirit of the Witch. I'm really enjoying it so far, there's a few times though that Grimassi gets a little carried away with his references he uses in different chapters.

The first book I ever picked up on Wicca/Witchcraft was Ravenwolf's To Ride a Silver Broomstick. It was okay, if not a little fluffy. I had also done a lot of online research beforehand, so I knew the basics. After that, I ended picking up To Stir a Magick Cauldron and Fiona Horne's Magickal Journey. Unfortunately, most of the books I seem to pick up seem to either be fluffy, or written in a "you shall do it this way and not any other way" tone. Some stuff is good, but just take everything with a grain of salt. It also helps to take from a book what is useful to you, and add that to your magickal practices.

I made it through Cunningham's textbook mentality, so I guess I'm on the right path
I have to agree though, if you're just starting out or curious, his books are an easy read.