Where can I find a geographic plot of the economic density 
of the united states.  For instance, if there are three 
businesses in a given region, the plotted value for that region
should reflect the sum of the market values of those businesses
at a specific time no older than 1/1/2000.  Each region 
should contain no more than 50,000 residents.  I also need the
the actual data files used to create the plot.

1) if you want a density measure, you will need to divide total value by land 
area.

2)I think you are unlikely to find a data source that is able to disaggregate 
market value by business location.  How, for example, would you allocate the 
market value of a buisness that has it's headquarters in one region, 
manufacturing in a second, and distribution center in a third (particularly 
when one or more of these is located outside of the US?


3) Why not use household income as a proxy for the value of businesses in a 
region-- at the scale of the entire US, your "Regions" should be large enough 
that the results would be fairly close.  This ought to be a standard report 
from any demographic service -- take a look at the web sites for claritas and 
mapinfo.

this answer would come from a cross tab of the consumer expenditure survey and
the current popultion survey - as such you would use buying power of each
consumer relative to their earned income.  A market value for a region would
depend on the business involved and the likely expenditures for consumers for
that region.