Where did your most passionate users come from?
imp: I've had success with domain-specific forums.  If your product really is something that people can get passionate about and you present your website in a non-spammy way, there's a chance that you'll get initial traffic and then eventually the members will spread the word about your site to other forums they're members of.For your project, I would suggest having a no-signup live demo that they can use right away.  No one will get passionate about a landing page.  That might be useful for gaging interest and collecting emails, but if you can't solve someone's problem on their first visit (or at least make it clear how you could) then it's going to be hard to turn them into a passionate user.