Incentivize your current members to bring in new ones. Pay them for referrals. It's the best way to have happy members bring in qualified leads.

Also, leverage your current membership by having them articulate their experience. Have them write testimonials, do short video interviews (can be done with just an iPhone!), and take pictures to share on any social channel you have.

I always tell founders to take what's working, what's great, and "unwrap" it for the world. That means to have your "users" document the things they enjoy for you. Have a photo contest. Throw an appreciation event. Run a twitter #hashtag promotion that encourages members to tweet about you.

All in the interest of leverage THEIR social influence and personal networks to spread awareness. Referral and social proof acquisition is cheaper than all the other alternatives.