Facebook, Twitter, MySpace, and many others. All of these Social Networks have their perks and downfalls depending on your usage. But for you, your business, social networks can be a benefit.
You can market your blog through Facebook and Twitter. Do not underestimate the use of TinyURL to link your blog through Twitter. Try using the website marker in the Facebook profile to bring people to your site, and any other sites you have a need with.
Now MySpace. Not the best social tool in my opinion but it works well for a free site, that allows for a quick connection to a large population. Use the messaging tool to message out promotions, events, and other mass information.
LinkedIn is one of my favorite Social Tools. It allows for a professional connection with proper introductions. It gives recommendations, profiles, and basically an online Resume.
Think of the social tools you use, how do you use them, and what do they do best for you?