Many investors know about the key metrics that provide clues about the U.S. economy's health, and where it's likely to head in the near term. Retail sales, housing starts, UPS (NYSE: UPS) and Fed Ex (NYSE: FDX) deliveries and, of course, those infamous corrugated box orders, all provide clues about demand at the retail and wholesale levels, and are positively correlated with increases in U.S. GDP.

What's another metric worth monitoring? Office rents -- and here, like the recent statistics reported for the above metrics, the numbers are not good.

Office rent charges per square foot in Midtown Manhattan, London's West End, and Central Tokyo fell in Q3 for the first time since 2002, a report from CB Richard Ellis indicated Tuesday (pdf).

In New York, Midtown Manhattan office rents fell 2.7% to $98.08 per square foot. Midtown Manhattan includes the headquarters of many of the world's multinational corporations and the Broadway theater district, but does not include the Wall Street financial district, which is located in Lower Manhattan.

In London's West End, occupancy costs declined 5.1% to $248.66 per square foot. In Central Tokyo, costs dropped 5.3% to $184.26 per square foot.

Economist Richard Felson told BloggingStocks Tuesday the fact that rents are declining the world's top three financial centers for the time since 2002 is not a good sign. "It's further evidence of the spread of the recession," Felson said. "Very rarely do you see rates in all three cities declining at the same time. Then again, very rarely do you see all three regional economies in recession at the same time, either, which shows you the fix we're in."

In the wake of Wall Street's recent tumble, several cities have started vying for New York's position as the center of worldwide finance. In Shanghai, for example, some investors have noted that, in spite of the city's relative inexperience in the world of high finance, it is swimming in cash. Tokyo, meanwhile, is working on rearranging its regulatory structure in an attempt to make its markets more attractive to international investors.

Perhaps the most interesting competitor for the throne of worldwide financial center is Dubai. Currently in the middle of a massive construction boom, the city has taken a variety of steps to make itself attractive to foreign workers, including relaxing Islamic law and creating so-called "free zones," where taxes are greatly reduced. On the other hand, Dubai has a mean humidity of over 60% and several months where the average temperatures top 100° F. Of course, if everything was based on climate, the worldwide financial center would probably be in the South of France!

While it's hard to imagine New York ceding its position at the heart of worldwide finance, the same could once have been said of Venice or London. The one constant in world history is that nothing lasts forever, and countries that fail to remain competitive do so at their peril. While we wait to see the future of New York, I'm going to try to imagine Jim Cramer in a keffiyah!

I've just returned from the World Money Show, where some 10,000+ investors gathered to learn about global investing. I had a chance to meet with many of the advisors featured at the show, and I have been highlighting some of their favorite investment ideas. To view all of the stocks featured in this special global report, click here.

"As we head into 2007, some of the songs from 2006 will remain the same, chief among them the thirst for large-cap stocks in the established markets of the U.S., Europe, and Japan," says mutual fund and ETF expert Jim Lowell. "Of those three marketplaces, one stands out as not having participated in last year's global rally; Japan.

"Such a perspective isn't shared by any of its Pacific Rim neighbors or emerging market players, all of which have enjoyed nearly nonstop gains for several years in a row, and most of which are trading at recent or historical highs. Overall, that makes Japan interesting from both a valuation and a contrarian perspective."

Here, the editor of The Forbes ETF Advisor reviews his buy-rated Japan exchange-traded funds:

"Japan, the world's second largest economy, continues to recover nicely from its epic recession. It also continues to benefit from its location. The iShares MSCI Japan Index (NYSE:EWJ) covers nearly the entire market capitalization of the Japanese markets, but the ETF correlates most closely with the Nikkei 225 (Japan's equivalent to our S&P 500).

"Its top holdings include stocks such as Toyota Motor (NYSE:TM) and Sony (NYSE:SNE). Blue chips in the land of the rising sun haven't always risen; but I think there time has come.