I can't begin to tell you how many requests I get from people who are looking for someone to write their business plan.  The request usually starts with something like "I've got this fantastic widget I've created that is going to change the world, but I need a business plan so I can pitch to venture capital, and I don't know anything about business."  Let me say this as strongly as I can.  If you don't know anything about business and you need to ask someone to write your business plan, you probably shouldn't be going into business.  It's as simple as that.  Here are the reasons why I think you need to write your own plan (with help from your partners and stakeholders).

1. No one knows your business concept as well as you do, and no one has the passion for it that you do.  Mary from XYZ Consulting writes these plans in her sleep--do you really think she'll convey the appropriate amount of enthusiasm for your business?
2. Starting any business is fairly complex, so working through the analysis involved in a business plan is a reality check - do you really want to do this?
3. If your banker or investor finds out that you didn't write the plan (and canned plans are easy to spot), how much credibility will you have with them?  They want to know that they're investing their money with someone who really understands their business.

Writing a business plan is hard work, but if it's your business, you had better get used to hard work.  Write your own plan and you'll really get to know your business.  It will pay off --I promise.