With the current financial crisis, the government has an urgent need to increase revenues. At the same time, taxpayers struggling in the current economy don't need to have their taxes raised in order to provide this revenue.
But two obvious means of quickly generating a healthy amount of revenue have never been considered.
The legalization of drugs and prostitution in all fifty states. Making these two things legal would subject the billions of dollars already spent on these things to taxation, both from customers and through licensing and operating fees from the businesses.
It would also allow the tax dollars now allotted to law enforcement and the criminal justice system to be used elsewhere more efficiently.
I'm not holding my breath that this will ever happen, however, unfortunately.