An article on SEOmoz written by Jane, 'How to Leverage Web 2.0 & Social Media Sites to Market Your Brand & Control Your Message' covers about thirty sites that one can make use of for marketing.
Jane says about the article:
Nearly everyone who reads this article probably knows what most of the following websites do. What we've looked at is:
The site's "About us" information… or its meta description. Or its littering of randomly placed instructions.
Whether a user's experience on the site is the same as (similar to… somewhat in the ballpark of…) that which its developers claim it should be.
How useful the site is as a business tool. Can you use any of these sites for your commercial benefit, or are they serving as little more than mindless entertainment?
This article is a single resource compiling useful information. It is infact a must read for all social media enthusiasts.