Almost half of the money spent by the federal government is for entitlement programs.
From Federal entitlement programs more costly :
Social Security, Medicare and Medicaid accounted for more than $1 trillion in the 2004 budget year, according to the Consolidated Federal Funds Report released Tuesday by the Census Bureau. Overall federal spending was $2.2 trillion, an increase of 5 percent from 2003.
Also see the charts and tables at Federal Budget and Spending for various spending categories.
I hope this information is helpful for you.