Amazon has always been one of the pioneers in terms of Social Media Marketing. Amazon was one of the first to create Web2.0 tools, with product review tools.
Recently they have started twittering their Deal of the Day. This is slowly becoming more specialized with AmazonMP3 Deal of the Day as well. They join Woot, as examples of online e-commerce site spruiking their daily specials online. These are two great examples of companies creating their own platforms of communication (Platform Creation) with consumers. Thanks to Marketing Geek for the tip and Get Elastic for the Woot example.