TaxProf has a good summary of resources and commentary on H.R. 1956, the bill now pending in the House that would gut the ability of the states to tax corporate income. See my previous comments here.
Among the material that can be found there is a link to the National Governors' Association's report, Impact of H.R. 1956, Business Activity Tax Simplification Act of 2005, on States. According to the report, in 2007 alone, the states would collectively lose almost $8 Billion in revenue. By way of example, Maryland would lose $106.4 Million, representing 26.8% of its corporate income tax revenue. The CBO reports more modest, but still significant, revenue losses of a billion dollars in the first year of enactment, growing to $3 Billion annually by 2011.
H.R. 1956 is a bad bill. Perhaps worse than the substance of the bill is its dishonesty, being cast as a "tax simplification" measure.
Don't be fooled.