A few tips from me-

Try your local craigslist....keep the add simple and on point.

Myspace ads- If you have a myspace site, post your banner on your page and add the classifieds application...post new bulletins each week or daily promoting different areas of your site.

Teachstreet.com- If you teach on your site...this is a great site for posting classes and lessons, even have badges you can put on your site, and you can also link that profile to craigslist.

Google- google has a free add url page to submit your sites...Ive gotten a few hits that way

Word of Mouth- once word gets around about how great your site is...people will come.

Facebook- Start a site fan page. I did that and have a few fans...I mainly use it for updates on the site.

Mainting and running a website is a lot of work..and if you arent going to be commited to it 100% then it will avail you nothing.

Just from the suggestions above...Ive gotten quite a few new members in the past week alone.