Social Media

Well it isnt directly SEO but it goes right along with it. Social Media networks are huge and can be of great potential when designing your SEO plan.
Social Media networks can mean using Twitter or Facebook to your advantage or even using Social Bookmarking such as Digg or Delicious. It will take a lot of work to fully optimize these resources though. You will have to build your relationships from within your network, but once you do you will see your website traffic sky rocket.
Dont expect to join one of these websites with the goal of advertising though. It will be dead obvious and you probably won't get the attention you want. Instead be clever in how you advertise, build your relationships, then give advice. Don't spam either. Spamming your site on such services will not help you gain traffic. It is very unprofessional and many people will simply ignore your site for such reasons.
You need good content. Once you have a good amount of great content people will begin visiting your site and re-posting and sharing your information. They will provide links back to your site which will help your page rank. They will talk among the people in the niche and that will be your publicity.
This will be a time consuming process that will take dedication but the end results are more than worth it. Best of all it is free advertising that can be targeted within your specific niche market.