If you stick with a regular external Bluetooth keyboard, be sure to invest in a good case that will allow you to prop up the iPad. We reviewed quite a few of them last month. Apple's basic case for $39.99 gets the job done for landscape mode, but it has a tendency to wobble and tip over when you're tapping on the screen. Invest $20 more, and the Incase Convertible Book Jacket for $59.99 provides more protection and a sturdier stand. Then there's the DODOcase, a favorite at TUAW. Starting at $54.95, it not only looks great, but it provides good protection as well.
If you prefer to type in portrait mode, Twelve South's portable Compass Stand is $39.95 and is easy to toss in a bag. Griffin's Loop Stand is $10 less, but you'll get a bit more bulk. Or, you can go the Erica Sadun route and use a basic wire study stand for both portrait and landscape modes.
Don't forget bags. There are a number of good bags out there that will hold your iPad, accessories, and a few books as well. Our own Steve Sande reviewed the Booq Boa, and it has enough room to tuck a keyboard in that front pocket. You can never go wrong with a Waterfield or a Tom Bihn bag, but make sure the iPad compartment is large enough to hold your iPad inside the case you selected.
Apps for the writer
While I am a fan of Google's products, I suggest staying away from the iPad-enabled version of Google Docs for your writing. Check out a dedicated iPad word processor. Pages is basic enough, but it lacks a number of features (edit: but, it does have word count now!). Check out Quickoffice ($14.99) or Documents To Go ($9.99) for iPad. Both will give you the most bang for your buck and can be synced with Google Docs and a number of other servers.
Set up an account with Dropbox if you haven't done so already. It's free for the first 2 GB of storage and will also sync back to your desktop and interact with certain writing programs on the Mac. You can do the same with MobileMe's iDisk as well if you're a subscriber.
Simplenote is a free app that will enable you to sync not just to any web browser, but it will also sync with Scrivener -- in my opinion, the best program for novelists and screenwriters on the Mac. Notebooks for iPad ($8.99) is a great program that will let you sort your writing into different "notebooks," and it lets you swipe back and forth between documents in said notebook; it also syncs with Scrivener. My own writing uses a combination of Notebooks and Quickoffice, using both Google Docs and Dropbox for sync and sharing purposes.
If you want a basic app for getting your thoughts down, there's iA Writer ($4.99), complete with a version for the Mac coming soon, and PlainText (free), both of which work beautifully with Dropbox syncing.
Once you've got those under your belt, go set up and type away on your iPad! It's compact, and you'll find that by focusing on just the open app, you'll be able to get more writing done.