My main requirement is a desk and a comfortable chair. It is nice if you can afford the space for a second chair, where you can have a friend sit and talk to you. I also require file cabinets to store all of the papers that I have accumulated. My plan is to scan them but I still need a place to store everything in the mean time, plus somewhere to store original documents that I plan on keeping long-term.
You will obviously need a trash can and a stapler, a ruler for holding your place in a document, maybe a magnifying glass and some sticky notes. I also keep a few maps handy, both modern and historical, from the areas I am researching. I also have any genealogy reference books that I own, within arms reach. If you cannot get to something easily, you might as well not have it at all.
I have my scanner, and an external hard drive to back up my laptop at least once a month. I also use a free service called Dropbox that allows me to upload files online that I can view on any computer; anywhere I can get an Internet connection. This is great for using the same files on your home computer, work computer, the computer at the local archives, even on your iPhone! I also use Dropbox as an additional backup for my critical files, to keep a safe copy outside of my house.
Other things...you always need basic office supplies; pencils, paper, staples, paperclips, file folders, etc. Stepping up from basic supplies, I actually bought a rubber stamp with my address, website address, email, etc. so that I can just stamp copies that I send other people, so they know where it came from. This saves time and helps give credit where credit is due.
I have wireless internet set up in my house already and my laptop connects to it automatically. I try to plug my laptop into a surge protector when I use it at home, just in case of a power surge. It might seem silly but I also like to keep coasters and paper towels nearby, to both prevent and clean up any drink spillage! You would be surprised how many times I knock over my Dr. Pepper!
Two things I do not recommend are televisions and radios. It is very easy to make mistakes when your attention is divided so I actually like to do my genealogy work in silence. I typically work after my wife and kids go to bed so that my attention is pretty much undivided. As a matter of fact, I turn off my email program so that I do not get interrupted by incoming mail! That might seem extreme but quiet and focus are keys to being a good genealogist. Why else do you think the librarian shushes you at the library?
As for fun stuff, I have a glass display case where I showcase some of the physical items I have discovered over the years, like my great-grandmother's broach. I trade the items in and out once in awhile to keep things interesting. I also have a few family photos, my college diploma and my wife's wedding portrait to cover the walls...all things that inspire me. There are also a few autographed football helmets that I have collected over the years...I was a big Joe Montana fan despite loving the Redskins.
Keep your space light and airy, paint the walls a soothing color...mine are a golden yellow and it works great with the room. The most important thing is to make a space that you want to be in, somewhere to serve as your retreat. You should want to be in the space, it should be functional, and everything you need should be within reach.
You do not have to have a huge area, or spend a bunch of money, to make a great genealogy work space. As a matter of fact, the only money I spent in my new office was for the paint and a trash can. I already owned everything else; I just arranged it in the proper fashion. I am still a little short on time to use it right now, but I am sure that my new office will inspire many discoveries to come!