You may find that the easiest part is the actual writing of the plan. The real work comes in the data-gathering, which may take you a hundred hours or more, depending on what you already know or have researched. If your new venture is in an area where you've been working, you may already know about your customers, your suppliers, your marketing plan, your organizational structure, your financial and cash flow needs, equipment, inventory, and so on.
However, the best business plan template is that which meets all your business needs and requirements by offering you a high level of customization and a professional layout of all the content that you would like to include.
U.S. Census Bureau (census.gov): A source for a variety of useful statistics, especially the Economic Census that comes out every 5 years.
The best place to find web templates is to search on the Internet. There are many sites to search templates and they frequently provide good supplementary details and technical support. You can regularly see a sample of the template you are taking into consideration.