We are having some good success using Twitter.  Here is an article I found that has some good ideas too:  http://www.socialmediaexaminer.com/4-ways-to-use-twitter-to-capture-customers/  Hope the link still works.  Basically it talks about using twitter to promote contests and discount coupons to bring new customers in.  Also, using custom searches to find out who is talking about your product area and then replying to them with an offer or something.  Check it out.