Stock Market Power Rankings: Amazon Back on Top

Each week, I'm ranking the biggest companies that trade on U.S. exchanges based on their size ( market capitalization), momentum (total return over the past year), and recent news. Before we get to the rankings, a quick word on a major player.

We have a new name on top of the list this week, as Amazon.com (NASDAQ: AMZN) has seized the market-cap crown from Microsoft (NASDAQ: MSFT). Amazon is now the only company on the planet with a market cap north of $800 billion.

Using $800 billion as a high-water mark isn't as glitzy as $1 trillion, a market cap that Amazon briefly commanded last year and Apple (NASDAQ: AAPL) donned for several months before fears of shrinking iPhone sales roughed up the consumer-tech behemoth. Apple has gone from being the world's most valuable company to fourth among stateside-listed investments.