[Spiderden]

Posting on other forums with related content is n excellent way to find new members, not only are many of the members likely to have an interest in the content of your site, they are by definition into forums so they are perfect recruits. A simple sig link will suffice, if that's not allowed then a URL in your profile can work. Make quality interesting posts then people will check out your forum out of curiosity.

Another method that can prove effective in the early days if your forum S/W can handle it is to use quality news and blog feeds to post threads directly onto your forum, if you choose them well they can provide good thread starting material and also supply your site with a good scattering of relevant keywords.