Here are a few ideas... (I'm working on systematically implementing each one of them)...
Search engine optimization.
Social media (Facebook, Twitter, etc.)
Blog communities (mybloglog, blogcatalog, etc.)
RSS Feeds (Feedburner)
Social Bookmarking (check out onlywire.com)
Commenting on other's blogs.
Commenting on forums related to your topic.
Article marketing. (e-zine articles)
Video marketing (youtube, google video, etc.)
Guest post on other's blogs related to your subject.
Allow other bloggers to guest post on your blog.
That's just off the top of my head.