American Express's(AXP, Fortune 500) marketing team has been winning plaudits for its use of social networks since it took to Facebook to launch Small Business Saturday (a made-up holiday encouraging consumers to shop with local merchants) in 2010. The campaign went viral and helped connect buyers and sellers.
The financial services company continues to take advantage of such tools to promote its products. In 2011 it developed a social substitute for coupons: AmEx customers who link their cards to their Twitter, Foursquare, and Facebook accounts can get special discounts at participating stores. More recently #PassionProjects lets a community of creatives post and tweet about their passions for a chance at Kickstarter-style fundraising.
AmEx gets extra points for its leaders' commitment to social media. (It helps that CEO Ken Chenault is friends with Facebook operating chief Sheryl Sandberg.) --I.M.