When you run an email marketing campaign, we hope you're including links in that email that lead recipients back to your website -- to read more content, convert, whatever. When you take a look at email marketing as a source of traffic, you'll be able to see how much traffic is sent to your website due to email marketing campaigns you've sent out. That's how we found out, for instance, that driving blog email subscriptions was extremely important to the growth of a business blog -- because many of the visits we receive each month come from subscribers who get pinged in their inboxes that a new blog post is published, prompting a click through to the post! Just be sure to include tracking tokens in the links of your email, otherwise the clicks won't be properly bucketed under the email marketing source.
Facebook ads are a great way to get highly targeted traffic to your blog (landing page, fan page, what ever). Although not a free traffic source, it is a great one. The price is not very high and I think it is pretty acceptable considering that you can choose demographics of Facebook users that will see your ad. I had great success getting traffic that converts on one of my niche sites.
Beyond organic and direct traffic, you must understand the difference between all of your traffic sources and how traffic is classified. Most web analytics platforms, like Google Analytics, utilize an algorithm and flow chart based on the referring website or parameters set within the URL that determine the source of traffic. Here is a breakdown of all sources: