I just read "Running Lean" - by Ash Maurya. Founders; read it! If you are spending more than 20 minutes on your initial business model canvas, you are doing it wrong.
This video will show you how to capture your core business-model assumptions on a Lean Canvas in just 20 minutes.
Here is an Excel file with the canvas, which you can use to play around with: http://neoschronos.com/assets/business-model-canvas.xls
Start drafting! And remember: you HAVE to share each canvas you create with 1 other person at the minimum. Then you get started! :-)