UPDATE: This is a pretty dated article, and a lot of these sites are probably not worth your time, and may not even be in existence anymore. For an up-to-date list check out this site: http://www.prelovac.com/vladimir/top-list-of-social-media-sites
Below is a list of 100 social bookmarking sites for your blog. They are listed (roughly) in order of importance/ranking.
If you spend 15 minutes daily registering your blog with a few of the sites, you should discover that your blog is receiving a lot more traffic fairly soon.
How to Use Bookmarking Sites to Gain Links and Traffic explains how to use these sites to your advantage.
For more SEO tips, read my SEO Diva blog.