U.S. Census Bureau (census.gov): A source for a variety of useful statistics, especially the Economic Census that comes out every 5 years.
One key component critical to your success is scoping the competition. A business plan consultant studies the area where you will be located quite thoroughly. For example, if you plan on setting up a coffee shop on Main Street, or within the vicinity, the small business consultants you consult with will inquire about the number of existing coffee shops and the services they provide.
Internet Public Library - The Census Data and Demographics (ipl.org)/: An especially useful site that has links to information about countries other than the U.S.
The planning wizard makes it a snap to get started since you simply answer yes or no questions to create your custom business plan framework. Bplans.com offers free business plan samples and how-to articles as well as a wealth of other information. It is definitely worth taking the time to checkout. Microsoft Office Online Templates also has a variety of free templates to use with their products. The wizard indicates the information you need and you fill it in as you go.