Here are some private companies that may well end up being the growth stocks of the future. Sure, some of these may have questionable revenue models and would certainly be a risky investment, but they are all innovative and forward-thinking in my view. Start your homework now because they're likely to be fast movers if they do issue public stock. Some of these companies are already on their way to going public, but all have carved out a strong niche in their respective industries. Let's hear what you think, did I forget the next Google or include a company that will go the way of the landline phone?