This article from Mashable.com is a good overview of the choices and options facing start-ups in choosing what sort of business entity to form. This particular article focuses on the various flavors of Limited Liability Companies (LLCs) that exist in the U.S.
LLCs are often excellent entity choices for start-ups due to their flexibility, tax treatment, and ease of both set-up and administration. If you are thinking of starting a new business, this article is a good source of information on LLCs. It will arm you a good basis for discussion with your attorney (you do have a business attorney helping you, right?) about what choice of entity will make the most sense for the company you envision.