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.
Press for Success : Far be it from me to dampen your enthusiasm, but you should give yourself every opportunity for success. That's what the planning part of the process of creating your business plan will do. By the time you have pressed your way through it, you will not merely have some neatly arranged document to keep on file, you will have a working tool that addresses the essential factors that influence your future.
U.S. Census Bureau (census.gov): A source for a variety of useful statistics, especially the Economic Census that comes out every 5 years.
But your idea may be so new that you may also need to talk to potential customers, host some focus groups, talk to an ad agency, or maybe even make a prototype and float it past some people. Be prepared to spend the time. Remember, it's not about the Plan but the Planning.