National Budget Simulation
Awesome in the "I'm a geek and don't care" sorta way. Only thing it lacks is a "flat tax" option.
This simulation asks you to adjust spending and tax expenditures in the the 2006 budget proposed by the White House in order to achieve either a balanced budget or any other target deficit. In order to make the choices we face in the budget clearer, we assume that you make the adjustments all in one year."