The Pentagon receives the lion's share of the US tax payer's dollars.
36% goes to current military expenses. 18% goes to what's called "past military" which includes veteran's pensions and medical benefits.
The US spends more on its military than the following countries COMBINED: China, Russia, Britain, France, Japan, Germany, Saudi Arabia, South Korea, India, Brazil, Italy, Australia, Canada, the Netherlands, and Indonesia.
Where does the money go?
At least 25% - and some estimates are much higher - goes down a rat hole unaccounted for and never to been seen again. The above news report ran the day before September 11, 2001. The problem since then has become exponentially worse.
You can see the numbers here: