The New York Times has a neat little application that lets you decide how to balance the budget. Basically, it offers an array of programs to cut or taxes to raise, and lets you mix and match them until you balance the budget in 2015 (current projected shortfall: $418 billion) and 2030 (current projected shortfall: $1,345 billion).
One thing becomes very obvious, very quick, and that's that to make any dent in the deficit, you'll have to either raise taxes, or cut defense or entitlement spending. Eliminating earmarks, for example, only nets a savings of $14 billion dollars -- barely 1% of the 2030 shortfall. Reducing troops in Iraq to 30,000 by 2013, by contrast, nets a whopping $169 billion.
I was able to balance the 2015 budget with roughly a 50/50 balance of spending cuts and tax increases. To handle the much larger 2030 deficit, though, I had to resort to more tax hikes, changing the proportion to more like 70/30. Most of the spending reductions came from the defense department, mostly by shrinking the size of the armed forces (particularly the air force, navy, and nuclear arsenals) -- that got me almost $300 billion on its own. Other cuts included slashing farm subsidies and reducing social security benefits for high earners.
On the tax side of things, I returned investment and estate taxes to their Clinton-administration levels, raised the payroll tax cap, instituted a "millionaire's tax" (basically, adding another tax bracket that starts at $1,000,000), eliminated tax loopholes, and established a carbon tax and a tax on risky banks. Altogether, this would reduce our 2030 deficit to a mere $16 billion, while causing us to actually run a 2015 surplus of $269 billion dollars.
But that's just my plan. Go ahead, fiddle with it and try your own!