I definitely recommend Facebook, Twitter, Google +, Squidoo and Stumble Upon!! The key is the post consistently and post unique and useful info!
Well in my opinion. i think you should start with Facebook first. Then you can start trying out others like twitter.
Facebook is a best social networking site for business purpose now a days.and if you want a lot's of traffic then you should do seo for your site.
Well as I already Mentioned although Facebook and Twitter are two big things for social media optimization yet if you take a closer look on LinkedIn it has greatest business development opportunities and can be considered a proper channel.