The most useful marketing tool ever has come about through social media. What is social media? Sites like facebook.com, linkedin.com, twitter.com, del.icio.us, digg.com, and youtube.com just to name a few, are all what are called social networking or social bookmarking sites. They are all places to interact with other people and share information and ideas. You can also market your products or sites through these sites with millions of other users.
Signing up for an account and using these sites is free. Every site that gives you the opportunity to interact with large groups of people at no charge are beneficial for including links back to your site or product pages.
Many of these sites like del.icio.us, and digg.com link back to information within your site or blog. Writing unique articles with information related to your site or product and then networking the article to to these sites will also get people backto your site or product.