Not a new idea, by any means, but one I thought I'd put back up here for people starting out...

You can join Yahoo Groups for free, where there are hundreds of communities related in one way or another to your site.

When you post messages within the group, that message goes out to everyone in the group. Several of the groups I belong to have a membership in the 500-800 range.

Now, certainly I am not saying to spam members, I'm just saying that, if you can provide posts that add content to that group, and sign the post with your URL, you'll pick up some traffic, for free.