Last year we forked over about $1.9 trillion to Uncle Sam (who then spent $2.3 trillion).
So where does all the money go? Lots of places, of course, but most of it goes to:
1. Department of Health and Human Services ($543 billion)
2. Social Security Administration ($530 billion)
3. Department of Defense ($437 billion)
4. Interest on Treasury debt ($321 billion)
For more, go to page 5 of this pdf file.