Sites that offer free traffic based on a number of different models.
Some pay people to surf, not the best quality traffic, but it's there.
Some do an exchange, for example:
You post ads on your website and get 100 views, they give you 50 views on other sites in the network.
And yet other, provide some other program or method for getting traffic to you for free. You just need to look into each, and see which is the best fit.
here's the links:
http://www.adleaf.comhttp://www.trafficzap.com