Lawyerist caters to our do-it-yourself impulses with an article on creating your own professional-looking letterhead:
While you may have to use a commercial printer for business cards, you do not necessarily need professionally-printed letterhead. If you already have a logo, you don’t even need professionally-designed letterhead; you can just DIY.
This is especially true when you consider that most correspondence never gets printed, and a lot of correspondence does not go out on letterhead in the first place. This makes DIY letterhead an increasingly defensible choice. Using resources like Typography for Lawyers, a few Word tips, and perhaps a bit of well-placed graphic design help, you can design your own letterhead.