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The variety of social media delivery mechanisms is increasing in leaps and bounds-Social Networking, Corporate Blogging, Online videos, Facebook Fan pages, Widgets, Microblogging, Twittering, Second Life, YouTube and Flickr are being used for marketing, branding and consumer engagement.
In this context, Peter Kim's 162 brands using social media for marketing [1] makes an interesting reference list.
Also worth reading:
An insider's guide to using Flickr [2] for marketing.