Be a real person. Create relationships with people online. There is so much spam floating around that you won't create buzz through the social networking sites if you just add to the noise. You need to provide real content (as has been said) and then engage in relationship with people. Comment on blogs that are in your business area, like other pages on Facebook and comment on them, say human things on Twitter instead of just linking back to your site. Leverage the fact that you're a small business with real people to make a real connection with people.