The most famous Social Network is Facebook. Facebook has more than 1 billion members and after Google has the biggest unique traffic. Facebook can bring all websites quality targeted traffic for doing nothing. You just need to create a Fan page for your business and promote it.
Promoting your fan page is very necessary at the beginning. This is because you have to gain at least 25 likes to change your address. When you create your fan page Facebook gives you their own address that will not be related with your business. After gaing the necessary 25 likes Facebook allows you to put your own targeted address.