Viral Marketing

C Eric Smith provides an overview of 3 online marketing techniques: Viral Marketing, Paid Search, and Affiliate/Referral sites:

Viral Marketing
Successful Viral Marketing campaigns have the following characteristics:
- Exclusivity and Community: "I've stumbled across something really cool, and I want to show my friends so they can be cool with me."
- Value with No Upfront Cost: People should get something out of it for free.
- Built-in referral mechanisms: Make it easy for people to refer others to your site and make it so that these referrels make the site more valuable to the referral. Carefully weigh the cost/benefit of referral incentive or reward systems
- Dynamic Offerings: encourage repeat visits by updating content regularly, and through periodic non-spammy newsletters. Consider running periodic specials or events
- Gauging Success : ask users how they found out about you, and check your logs often to see where the traffic is coming from.

Click-Through Rate/Paid Search
Google AdWords is a service that displays advertising links based on people's keyword searches. You bid on keywords and search phrases to have your ad appear on the search results page, and then you pay Google that amount per click on your ad. This takes a bit of trial and error and constant refinement and adjustment to optimize.

Affiliate/Referral Sales
Contact sites with higher traffic than you and offer them a share of the revenue you receive from customers that originated on the their site.