Social Media Mega List

The Social Media Mega List at Wikipedia gives tons of information on various social media sites, their enrollment numbers, and what niche they are focused towards.

Social media is an excellent tool for growing your site.  Sites like Twitter, MySpace, and Facebook have plenty of users that you can reach out to for growing your site.  Digg, StumbleUpon, and Reddit can bring you tons of new page views in a moment's notice.  Some sites may be more useful than others depending on your business strategy or your marketing niche.

What I suggest is start off with just one social media site.  Join up and learn how it works.  Then you can start to relay posts to your social media site, or send tweets to your blog posts.  Just start off to learn and grow your follower base.  Once you understand how the site works, you can start using it as a tool to grow your site.

Twitter is probably the easiest to start out on as it is the least complex of the major 3 social media sites.