If you look at their bookshelves, you might find it arguable that Pagans are "People of the book", though not in the same way that the phrase is usually used. In general, extensive reading is encouraged, or at least should be, by every Pagan group. It is important to get multiple viewpoints and accounts; this does help with Instant Witch Syndrome, though is by no means a cure (and can lead to MegaPagan Syndrome). Here's a somewhat loose list of reading I'd recommend to the beginner. If you find a book disagreeable, figure out why. I do fully support the idea that something might just "not feel right", but in my experience, there are often reasons for disliking a book.
Of course, there are also those who will tell you that all modern books are utter bovine scatology, and often start talking about the good old days when information was hard to find and was much better when it was found. I tend to roll my eyes at such suggestions — Bonewits' Commentary on Sturgeon's Law was alive and well long before the first New Age Fair, and a lot of medieval grimoires had a different reality map in mind.
Note: This list is oriented towards the Pagan with online experience; obviously, if I was giving a list to someone who didn't spend much time online I'd come up with something a bit different.
Read a basic book about Wicca, even if Wicca isn't your path, because Wicca dominates the modern Pagan movement. Also, some groups that claim to be reconstructionists just do dressed-up Wicca. Basic books on Wicca include Wicca: A Guide for the Solitary Practitioner by Scott Cunningham (the one I've actually read in full), The Spiral Dance by Starhawk, and To Ride a Silver Broomstick by Silver Ravenwolf. According to reviews (I've not read it), Teen Witch by Silver Ravenwolf seems to focus more on magic than religion, and so wouldn't be a top choice from
If you're set on a path other than Wicca, you may wish to dig up basic books on it. I will wish you good luck, though; many books dress up Wicca, make wild guesses, or both. You are often better off finding websites on the topic, such as Ar nDraiocht Fein's page at http://www.adf.org/, or the Church of All Worlds website at http://www.caw.org/. From there, you will often be able to find recommended reading lists and reviews of books (or at least know who to trust
in online reviews). If you're uncertain about your path, you can also do this, though you may find it more helpful to see how groups operate in the real world, or get the big picture.
Now, to help flesh out those basics books (particularly if you're only able to read just one), you should poke around (not necessarily slurp down wholesale) on some archive-type sites. The Witches' Voice, at http://www.witchvox.com/ is a prime resource in this way. More eclectic is the Pagan Library at http://www.paganlibrary.com/. Medea's Chariot, at http://www.medeaschariot.com/ is also rather eclectic. Daven's Journal, at http://www.davensjournal.com/, also has a variety of material. To get a different, semi-Pagan perspective that leads into the American Druid movements, read A Reformed Druid Anthology from the Reformed Druids of North America at http://www.student.carleton.edu/orgs/druids/ARDA/.
Now you should learn some about the Pagan movement's past. Drawing Down The Moon, by Margot Adler, is a good survey of Paganism up to about 1985 (it was written in 1975, updated in 1985, and then had the resources updated more recently).
A Community of Witches, by Helen A. Berger speaks more about the social growth of modern groups, discusses the lifecycle of a group, and demonstrates that the
Pagan movement is not the safe as the New Age movement (which almost makes up for her constantly confusing Neopaganism and Wicca). Isaac Bonewits' A Brief History of Witchcraft is almost certainly good (I've read its predecessors). There are some other books about history, but not having read them, I'll instead point you to online resources of historical interest. There is a good node on here about the Lesser Banishing Ritual of the Pentagram (particularly of interest to Wiccans, as it is one of the more obvious roots of their ritual), and Tim Maroney's essay on it at http://maroney.org/Essays/Pentagram_Ritual.html is worthwhile as well.
At Lysator, there is a Pagan-oriented ftp site; because it is somewhat stale (as ftp sites tend to be these days), it too is of historical interest: ftp://ftp.lysator.liu.se/pub/religion/neopagan/.
Margot Adler wrote "A Time For Truth" as part of her column for Beliefnet: http://about.beliefnet.com/frameset.asp?pageLoc=/story/40/story_4007_1.html&boardID=5077.
At Catalyst's Point, there is an essay about the Burning Times and appropriate historical context at http://www.catalystpoint.org/castings/burning.html.
While we're on the topic of history and the Burning Times, if you're one of those people who likes to feel persecuted, please pick up a copy of How To Stop Worrying and Start Living and stop whining constantly. Thank you.
Looking at history in a different light, you will probably want to read some mythology. There's Bullfinch's Mythology, of course, and many other collections (forms of which can be found online). Celtic mythology is harder to track down due to the lack of written records; Alias Mother Jonez is probably more expert in this area than I, but you'll want to look for the Tain and the Mabinogion at least, and will want to read different sources more than you'll need to with Greek mythology. To take a look at a syncretic view, read the Golden Bough. Also, read about the myth of syncretism at http://maroney.org/Essays/The_Problems_of_Syncretism.html.
Now, you ought to get some skepticism in you. Read some David Hume (you should be able to find some of his essays online easily). Go to the Skepdic (http://skepdic.com/) and read everything under a topic that would be of interest. Read up at CSICOP's site (http://www.csicop.org/) too. Now, back to Tim Maroney's site, since he has a lovely essay on skepticism and mysticism at http://maroney.org/Essays/The_Included_Middle.html
At this time, you might feel a little like Ed Gruberman, because I've been focusing on religious aspects, history, and then (of all things) skepticism, and you want to know how to do magic. Read Isaac Bonewits' book
Real Magic to explode your assumptions, particularly those you've
picked up from discussions of magic along the way. Now, you probably should also learn about the Western esoteric tradition, since that (or a distorted version thereof) is often the dominant paradigm. So get your hands on some Israel Regardie (the Tree of Life comes to mind rather strongly as a reasonable text), or perhaps some Dion Fortune. At this point I'd advise being careful with Aleister Crowley, simply because he tends to being deep, a trickster, and ha ha only serious. If you can't find those, perhaps you might find Liber Null rather interesting; though (supposedly) a text on
chaos magic, it is rather biased towards the Western occult view as compared to more state-of-the-art works. For sweetness and light, try Marion Weinstein’s Positive Magic; though fluffy, it isn't too far from what many people do. On E2, swankivy has written a Guide to Spellcasting that (to me) has some Wiccan overtones, but is a useful outline overall of ritual. Actually, swankivy, Wuukiee, and others (/msg me to be added) have written many good introductory Pagan nodes here on E2, and the aspiring Pagan would do well to look through their nodes.
Of course, there is one thing so vital that I forgot to mention it — find Pagan humor online and read it. There's a section the Pagan Library and a section at Medea's Chariot. Some more looking will turn up more. Why is reading Pagan humor so very important? Simply, it often conveys realities about Pagan practice and the Pagan viewpoint much better than anything else.
Now, this is just an introductory list, and one focusing on the basics of the religious/magical side of things. For instance, if I were making suggestions for someone wanting to be in a clergy position (not merely in the sense that each person is a Priest/ess), I might recommend learning group dynamics, diplomacy, financial management, counseling, and how to make ritual accessible.
Updated to note that swankivy simply had a (to me) Wiccan-like viewpoint rather than a Wiccan viewpoint.
Updated to note that humor is very, very useful.
Updated to make what swankivy had done clearer.