They look to be straight out of Star Trek's Enterprise, but Citigroup's telepresence centers bring executives from Hong Kong, London, New York and Mexico face to face at a moment's notice, and helped the bank reduce carbon emissions from business air travel by 31 percent from 2008 to 2009.

That's an impressive number, and a small part of why Citi topped the Money Center category in BTN's first ranking of America's Greenest Banks.

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