I don't think that's really what you want. Consider the following:
1. If a source of traffic is free, everyone will have it, thus reducing the likelihood that it will be effective for anyone
2. The quality of traffic is more important than quantity in most instances. Try selling snow cones at an eskimo convention
3. Free is usually costly, but in time not money.
Take a look at this picture: http://i.imgur.com/MA3YeuX.jpg. That's how many weeks you have in your life if you're 25. Do you really want to spend 25, 50 or 100 of those dots getting traffic to your site?
If you can find out the lifetime value of a customer (assuming you do have a product) and make the leap to controllable (usually paid) traffic, you will have effectively taken the red pill, matrix style.