Well, I'll start the ball rolling ...
The internet is a very organic beast, and its forms and features are changing all the time. What works now might not work at all in 6 months' time.
I ran a site about motorhomes for a while, and the best marketing I ever did was to join a lively online forum for motorhomes. I would post there often, offering help and welcome to new members. I even wrote a couple of articles for the site, attempting to help newcomers to the hobby. I would also spot a news item come up on the site, quickly write a blog post about it, and then join in the discussion, saying something like: "I've just blogged about this - click >> here "
Because of this, I became a trusted member, and got a huge amount of traffic (and income from PPC adverts) from the links in my signature. You have to be careful not to be seen as a spammer, which is why I built up a reputation on the site first, and then added the link to my sig.
Obviously, the use of social networking sites like Facebook and Twitter is a must. Again, post regular updates, and try to make them relevant, with links back to your site.
I'm sure there's so much more to say about this.
Gerald