I did a quick calculation this morning using stats from the World Bank Web site. The $75 billion we're spending on the war is equal to the gross domestic product of the world's poorest 58 countries combined.
With the $75 billion, we could easily put an expedition on Mars or build a moon base, send an unmanned probe to Alpha Centauri and build a space plane that won't explode.
We could build a 300 mph mag-lev train system connecting a number of major U.S. cities.
We could build a wind and solar power generating system which could power New York City and much of the East Coast forever.
We could ensure that no one in the United States ever goes hungry again.
Though this money is gone, I leave in your mind the truly awesome economic power we wield and what we could accomplish in the spirit of planetary enrichment.