Adjusting for Inflation, Apple Still isn't More Valuable Than Microsoft Once Was
Apple managed to keep the momentum going for a little while today as the company's stock surged to a high of $674.88, though it's currently trading at around $657. It doesn't matter though, the company is worth hundreds of billions of dollars, and bested a record set by rival Microsoft on December 30, 1999 when it was valued at $620.58 billion at the closing bell.

Image Credit: Flickr (rebelpilot)
That's mighty impressive, though there's a caveat. If you factor in inflation, Microsoft would still hold the record, and by a large margin. Adjusted for today's dollar, Microsoft's value in 1999 would have been worth somewhere in the neighborhood of $850 billion today. Microsoft benefited from the Internet boom more than Apple did at the time, and there was no such thing as an iPhone or iPad tablet back then.
Things have changed in the past 13 years, obviously. Microsoft's market cap today is around $258 billion, which is less than half of Apple's. It wouldn't be surprising to see Apple set another record following the iPhone 5 launch, assuming it's a successful one.