Don't Leave Your Portfolio Without American Express

Editor's Note: Jon D. Markman writes a weekly column for CNBC on MSN Money that is republished here on TheStreet.com.

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Investors looking for the best "green" investment in the stock market right now need look no farther than their wallets. Or the wallets of their bosses. Because it's none other than the king of credit cards, the emerald-hued financial-services provider American Express(AXP Quote).

One of the most universally appealing corporate brands in the world -- the very symbol of U.S. financial ambition and might from Manhattan to Mumbai -- American Express has also somehow become one of the cheapest and most disrespected stocks in the entire Dow Jones Industrial Average. The disconnect between its real value and the market's opinion at the moment is loony and unlikely to last, so file this one under "opportunity of a lifetime," and get ready to cash in.

Here's the deal: There is a school of thought in some morose corners of Wall Street that the residential real-estate slowdown, the subprime mortgage meltdown and the U.S. dollar fall-down will combine over the next few months in a swirling vortex of pain for the American consumer. This view holds that Americans will abruptly stop spending on travel, electronics and clothes because they have to set more aside each month for house payments, gasoline, bankruptcy attorney fees and antidepressants.

The facts don't bear out the bears' point of view, as you'll see in a moment. But that's OK, because this view has created an ideal chance to steal the stock. With American Express currently trading at $65 after a quick bump higher this week amid a rare spurt of optimism, I believe shares can shoot to $80 over the next 15 months if a couple of things go right -- a 23% move.

Undervalued Franchise

Part of the problem is that the market doesn't seem to know how it should set a value of credit card networks these days. Consider this paradox: Investors have given youthful rival MasterCard(MA Quote) valuations ranging from 15 times earnings to 30 times earnings since it went public last year.