Great article on forming a business (quickly) from Adam Warner.
One of the biggest things I try to tell people is to hire an attorney that specializes in business law *BEFORE* you organize your business. They are able to advise you on the best structure for your business and the best state to be organized in. Most corporations are registered in the state of Delaware for a variety of reasons even though they operate in another state.
Another thing I recommend is finding an accountant before you organize your company as well, as they will also be able to provide tax advice to you before you get in way over your head. It’s better to put together a strategy for paying taxes and understanding tax liabilities before you get started, otherwise you’ll find yourself with some issues when tax preparation season rolls around.