Optional, but nice.  I still prefer drawing while sitting on the couch, but I also have a crappy chair for my drafting table.  Any table will work just fine as a workspace, but it's useful to have one that tilts and can also support a flexible desk lamp for good light.  Good Christmas or birthday present, if you have the room for one.

I am very fortunate to have cabbaged onto a nice homemade light table.  I also work with huge dining table sized light tables, so I am doubly blessed.  I've seen small light boxes sold at an art store for $80 or $90, but you can probably figure out an easy way to make one for much less.  Another easy and very cheap substitute is a sunlit window - just tape your sketch to the glass with masking tape and draw until the sunlight shifts.  You can also use carbon paper or graphite paper for transferring sketches, or even sneaker and cheaper - take a soft pencil and shade the entire back of your sketch.  Then trace over the linework onto a fresh page, and the graphite on the back of the sketch will transfer to the new sheet.

Accept the fact that when you copy a sketch or transfer it, the copy will never look as good as the original, or be exact in every detail.  It's evil, but true.  But it's still a good idea to copy sketches for final drawings, because if you happen to screw up you can always go back to the original sketch and make another copy.

To me, this stuff seems ridiculously expensive at $4-5 for five 9x12 sheets, but it is useful for transferring a sketch when I can't use my light table (for example onto illustration board), and the sheets are reusable.  Comes in different colors, including white.

A must-have for inking and painting.

Just a place to store finished drawings flat and out of harm's way.  Take them out of your sketchpad (the pencil shading will get smudged beyond recognition after a while) and keep them carefully, away from feet and soda and food.  I have 2 large cardboard cylinders that I store my finished work in, which has the advantages of being very portable and the disadvantage of making my artwork curl up if stored for long periods of time.

This was something my sister started and has proved to be a very good idea.  She would cut out her finished drawings, or parts of her drawings that she liked, and paste them in a scrapbook with the date they were drawn and any thoughts she had about the work.  It's really cool to go back and look at how your drawings have progressed over the years - what you learned and where and how it affected your art.  Plus it's a great way to keep all those old drawings organized and safe.  You can also recycle old ideas that you had years ago, but didn't have the skill to do properly.

Use rubber cement.  It won't warp the paper like Elmer's glue, and you can also remove the drawings if you are careful.

Cut out things that inspire you and paste them in the scrapbook.  If it's a face in a magazine or a picture of a painting of a horse - whatever.  Save it.  You might use it later.

Keeps pencil drawings from smudging, and sometimes good to apply to pencil sketches before working with another media.  Hairspray is a cheaper alternative.

This can be just a regular clipboard, or one of the bigger ones you can get at an art store.  The basic idea is that it's a portable hard surface.  If you take your drawings out of your sketchbook, or if you work with loose sheets of paper, this is a good thing to have.

I find it helpful to pin my unfinished work up on a wall or bulletin board when I'm not working on it.  If I keep it where I can see it, I can spot mistakes or proportion problems I would otherwise have missed.  It's also a good reminder so you don't forget about any drawings you intended to finish.

Be careful not to post your unfinished artwork in direct sunlight.  The sunlight will effect the paper and graphite and when you go back to complete the piece you may have trouble getting the new sections to match the old.

Sometimes the only way you can get a pose right is to model it yourself.  Mirrors are good for helping with expressions, shading, proportions, positions - in short, just about everything.  Get a cheapie full length mirror and perhaps a smaller hand mirror.

If you wear a new white shirt for inking or painting, you deserve a stain.

Obviously you'll also need a computer for this.  I love my scanner.  They are remarkably affordable - you can get a nice one for less than $100.  Not only will this allow you to post drawings on your webpage or get a page at Elfwood (which has been a wonderful growing experience for me), but you can use the scans in computer programs like Photoshop or Paint Shop Pro and experiment with your drawings.  You can also scan in a drawing and print out a copy to color without screwing up the original.  It's possible to go to a copy shop like Kinko's and use their scanner, but at $15 a pop it's much more economical to just buy your own or use a friend's.

It's not a bad idea to invest in some good books with lots of pictures if you are interested in perfecting details or drawing accurate depictions.  A sense of realism is important in art, even fantasy art.  If you are interested in drawing wolves (which most people aren't likely to get a chance to study in real life), get a book on wolves.  Learn about what you are drawing.  In my collection I have books on armor, medieval life, castles, cathedrals, animals, forests - whatever happens to strike my fancy that I want to learn about.  I just make sure I get books with good pictures, so I can also use them for art.  I love Barnes & Noble because they have a selection of reduced books on a variety of subjects - I can usually find at least one that would be useful.

Magazines like National Geographic or Smithsonian can also be excellent for reference.  If you see a good picture of something, try to get a copy to save.  Also a good source of reference: the web.  You can assemble a nice collection of various images - just be careful to record where they came from, or keep a bookmark file.

It's important to realize that there's a difference between using something for reference and copying.  Copying straight from another artist's work or a photo can be great practice, but don't try to pass off someone else's work as your own, even under the blanket term 'fanfic' or 'fanart'!  Someone, somewhere will point out that the piece is not original, and it will have an impact on your credibility as an artist.  People will wonder if other drawings are original, or if your only artistic talent lies in passing off someone else's work as your own.  Always, always tell people specifically what you used for a reference, and if you copied or modified it.  People don't like to be tricked.  Avoid 'stealing' poses, details, or drawing styles that can be linked back to another artist, and always give credit if you do.

Personally, I don't understand why someone would waste their time and effort copying another artist's work.  What sort of challenge is it to draw something that is right underneath your nose?  Of course, I had the same attitude to drawing from life or photo, so don't take me too seriously.  I copied Disney animation cells when I was 12-14 and it was helpful, but I did them for the learning value only, I never attempted to pass them off as my own work, and I wasn't all that proud of the result because I copied instead of drawing from my own imagination.  Of course, the whole idea of fanfic is based on stealing.  There's nothing wrong with drawing Disney's Gargoyles, Pokemon, Sailor Moon, Elfquest, etc., but be sure to make the distinction between an original drawing of a character in a distinctive style, and a copy of another artist's rendering.  Yes, there is a big difference.  Give credit where credit is due, and be honest.

I'm mentioning this not only because it's a personal pet peeve, but because it can have legal ramifications as well.  You can get sued for copying someone's work and passing it off as your own.

Books on my bookshelf:

Drawing Human Anatomy by Giovanni Civardi

The only bummer part of this book is that he uses only male models because they have better muscular definition.  It's an unimposing paperback around 87 pages with clear and incredibly good drawings of human anatomy, as well as a sidebar that illustrates and describes the particular muscle groups and skeletal structure.  Lots of good, useful drawings, plus it doesn't have the $50 pricetag you will find on some anatomy books.  And it isn't cumbersome or heavy, so you can easily take it with you for reference.  There are other books by the same author - Drawing the Male Nude and Drawing the Female Nude - but I think this book is more useful because it focuses on the actual anatomy.
Encyclopedia of the Horse edited by Elwyn Hartley Edwards
Not as much anatomy as I would like, but lots and lots of pictures.  I have had this book since I was 10.
The Smithsonian Book of North American Mammals edited by Done E. Wilson and Sue Ruff
Expensive.  :-(  Lots of good pictures, though, and good descriptions.  Bought it to draw some mice for a Christmas present for my Aunt and Uncle.  I have no doubt that it will come in handy for many other drawings.  There are many other encyclopedias of animals, but I would try to get one that has actual pictures, instead of artist's drawings.  I got this one because it had lots of mice pictures.  If you are interested in a particular animal, you can probably get a book focusing on that animal and save yourself some money.
Western Forests by Stephen Whitney
General field guide, which means it basically has pictures of everything.
Wolves by Candace Savage
Trying to collect books that focus on an animal I will probably have in many drawings.  There are many books on wolves - flip through and find the one with the pictures you like the best.
Knights and Armor Coloring Book by A.G. Smith
Yes, this is a coloring book, but it does a great job of illustrating armor through the ages with clear line drawings.  Definitely not for big, fat crayolas and definitely something to keep away from young children and save for yourself.
The Known World Handbook
I very much doubt that you will be able to find this in bookstores, because it is the handbook for the SCA (Society for Creative Anachronism), a medieval recreation group.  It basically has a little bit of everything, from costuming to calligraphy to making chainmail and armor.  Fascinating and packed with useful information for anyone interested in medieval life, even if you aren't a member of the SCA.  Your best bet for getting one is to visit the SCA website and find a group near you (they are all over the world and the people are very friendly) and get one through them.  I am unsure if you can actually buy one from the website . . . but if you can get your hands on one they are pretty cool.
Big Cats: Kingdom of Might by Tom Brakefield
A good reference book for various large cats - lions, tigers, cheetahs, panthers, etc.  Lots of nice pictures.
Architecture of the World: Romanesque edited by Henri Stierlin
It's not a bad idea to get a book on architecture for compelling and accurate backgrounds.
Drawings of Mucha published by Dover
If you love Mucha or Art Nouveau, get this book.  It has some of his original pencil sketches, which are amazing to look at.
The Art Nouveau Style Book of Alphonse Mucha published by Dover
Another great volume of Mucha's works, focusing more on his decorative borders and design work.
The Medieval Soldier by Gerry Embleton and John Howe
Wonderful reference book.  Lots of incredible pictures of medieval garb, people in armor, people fighting with medieval weapons . . .  Absolutely amazing.  Also horribly expensive, and takes forever to ship.  :-P  Worth it, though.