I see many great ideas here and strongly agree Facebook is a great avenue.
Outside of all the "Online" answers I'd also suggest forming partnerships with other businesses in your local market that work with a similar audience. Do an open-house together, referral agreement or other simple partnership type of arrangements. I'd also suggest working with local realtors, PTA Moms and get active in the community events. These all helped me just as much locally as online advertising (if not more). Good Luck!