While it has become much less common, the local property tax rate was determined by:
tax rate = local government spending / total property values
Your individual tax bill would be then your property value times the tax rate. What if federal income tax rates were determined as
tax rate = federal government spending / total personal income
This would be a flat tax whose rate depended positively on the level of spending. For 2006, this calculation is (note that it is difficult to figure out what the government actually spends):
.261 = $2,866.7 /$10,983.4
I can think of several pros and cons to the current system, but my feeling is that this system would be an improvement.