There are many resources you can use, download, or buy at the store. You will spend a considerable amount of time researching, then writing business narrative section (Exective Summary, Business Description, Products/Services, Marketing, etc) this can take a few hours. But over 90% of people spend days on the financials section (Sales forecasts, Income/Expense, Break-Even analysis, etc).  I'm a fan of using online resources to make things a little easier. Below are the top three I've used with my clients listing the advantages and disadvantages I've found with each. If you have other tools you wish to share please do so in the comments section.

SBA.gov Business Plan Tool

• Advantages: It's free to use, save, print, download, change, all free with no hidden fees.  The Narrative sections are easy to use, just answer the questions in the box and it transfers them to a professional looking document (word or PDF). You can make it as simple as you want, it even gives you samples to each section so you have an idea of how it should read. It is quick, easy and free!
• Disadvantages: The Financials section has a standard template that cannot be modified, add or delete items. It's not easy to run the projections and break-even analysis. You cannot upload images, except for your logo on the first page. It does not create graphs, so the end document is not visually appealing. The system forces you to use a complex password that it is hard to remember (I still get locked out!).

SCORE.org Business Plan template

• Advantages: A downloadable guide that is as complete as complete can be. It has explanations for each section. It has added tools to work on financials and competitor analysis. If you are not in a rush, work through it and you will have a plan that paints a clear picture of your business opportunity.
• Disadvantages: This guide is quite thorough but if this is your first plan, it can be a little overwhelming to follow all the instructions and template worksheets. Some clients get frustrated with the process, and give up before you begin.

LivePlan.com Business Plan

• Advantages: LivePlan is business plan creation platform by Palo Alto software.  (The maker of Business Plan Pro, which you can still buy and install in your computer). The online version is offers a business pitch presentation, a scorecard to track your progress, and easy-to-do financials. It walks you through the plan step-by-step, offering a wide range of resources such as samples, videos, and other research tools along the way. It offers a way to share the work in progress with your partners, advisors, and other stakeholders.
• Disadvantages: It carries a monthly cost of $20 to access the browser based program. There are some discount codes such as "STARFISH_6MONTH" which gives you a 50% discount of six months for $60. After the initial six months, you will pay the regular monthly rate. Again, you would need to hurry up and complete it or it can cost you a lot of money. That may also be a benefit if it serves as a motivator to finish it.