What goals are you looking to accomplish?
There are often a lot of niche sites or local sites that you might want to try. Biznik for example is a professional networking site designed to connect local people so you can meet in person. Many are regional only so you'd have to find them in your area.
Do you have specific goals in mind? The reason I ask is because it seems like social networks would be a prime place for a real estate agent. I purchased a house in the last couple years and we found our agent by asking our friends if they knew anyone, if I talked to an agent regularly on Twitter or Facebook and trusted them there's a good chance I would go directly to them when I needed to buy a house, or recommend them when a friend asked me if I knew anyone.
Some sites are good at driving traffic, some are good for networking, some are good for brand awareness etc. specific goals might help narrow it down a bit.