Where is the best place to start if I want to write a business plan for my new company?

I need to apply for bank finance to help launch my new business, and my banker requires a business plan. Can anyone point me at the best place to start the process? Many thanks.
Update: Just wanted to add that I am in New Zealand, so would be good to get some kiwi input too :)
Update 2: Thanks for all the responses - much appreciated. Have found this link particularly helpful so far http://www.business.govt.nz/starting-up/writing-a-business-plan/free-business-plan-template
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