Facebook - get at fan page or your own page at least
Twitter - get an account and start following people that do things you like. Then use it too.
Yelp - http://www.yelp.com put your company on it.
YouTube - make a video and put it on you tube
Blog - Make a blog about what you do. Or what you like. Blogger, Wordpress,
LinkedIn - Join it
30 reasons for seo - http://www.inc.com/articles/2010/01/30-tips-for-using-social-media.html