Kevin Drum at CalPundit has posted an interesting article on the role of the government in the economy. I have to say that I agree with everything he said, with one caveat: the government's interventioned should be both limited and defined.
Completely free markets, without any external controls, are economic anarchy, no less than the lack of external controls on social behavior is political anarchy. No less than political anarchy leads often to political tyranny, as the strong sieze all of the real political power, so does economic anarchy lead to economic tyranny, as the rich and well-connected (and, normally, politically powerful) sieze all of the real economic power.
To prevent this, it is necessary to have external limiting mechanisms. The external controls for politics in the US were laid out in the Constitution: no direct taxes (limits Federal government's ability to raise funds, and thus its power); Senate must approve appointed officers and treaties, influences laws and budgets and has the sole power to remove a sitting President (all of which gave States the ability to limit Federal power); the States can call a Constitutional Convention at will; and as a final bulwark, the people have an unlimited right to own military arms. Of course, a combination of amendments and court decisions have limited and in some cases totally destroyed all of these limitations, except for the right of States to call a Convention.
The external controls for the economy were much less thoroughly documented in the Constitution. While power was given to the Federal government to regulate interstate commerce, and certain other powers (like not allowing a State to force traffic to pay excises at their ports just because it transits through the State's waterways) were also granted, these provisions were mainly intended to prevent interstate wars, rather than to actually regulate the economy. The only Constitutional provisions I can think of off the top of my head, which directly regulate the economy, were the ability to collect tarriffs and levy excises, to establish uniform weights and measures and to regulate the value of currency.
While I think that the government needs additional powers, not forseen by the Founders, I don't think that they should be available to the government except by amending the Constitution. Otherwise, the potential for abuse is too great. I think that we could come up with a list of such powers that the government needs: