MadCow said:
(corporations cause you to get taxed twice, once as business income and then once when you pay yourself)
This is true, if you create a corporation (Corp or Inc). For MOST businesses, especially small businesses, creating a limited liability company (Ltd or LLC) is a better choice. You are not taxed (at least in most states) at the corporate level. In New Jersey, for example, the income of the company simply passes through to the owners of the business and they report it on their own income tax, state and federal. If your state does not have an income tax, even better.
Also consider that forming a corporation brings with it certain business practices that a one or two-person operation, or even ten people, may not want to abide by, such a meeting requirements, quarterly tax filings, etc. An LLC is more flexible. And, if you would like to change from an LLC to a Corp later (like when you want to go public), you can, or you can simply form a parent corporation and sell the LLC to the parent, then take the parent public.
My advice, because it's the same advice I got from every attorney I spoke to about it, is form an LLC if you are a small business starting from scratch. With the acceptance of one-person LLCs in all states now (I might be wrong, Mass. may still require two people), it's the easiest way to protect yourself from liability and the most flexible of all company models.
Get yourself a book called "Starting a Limited Liability Company" by Martin M. Shenkman. The book is ugly on the outside, but has a great deal of good information, and I've looked at many books on the subject.
By the way, most states let you create an LLC on their Web sites. I did with mine and had everything done in about two hours (I printed everything off and made sure it was all correct, so I took a little longer than I would imagine it would take), and that included the Federal EIN from the IRS.
Also, look around at many of the companies you deal with every day. Many are LLCs. CNN, for example is a good example of an LLC, and so is Avis rent a car).
Good luck.