Yes, there is waste and money thrown at "pet projects", but the scale of it pales in comparison to defense, social security, medicare and debt financing. Also, federal employee pensions, which I forgot to mention earlier.
See below for more detail on how federal tax money is spent in the US. The Mandatory section is for spending commitments already mandated by law, meaning that Congress can't just decide not to pay without changing the existing laws, and even then may be forced to pay pre-existing commitments by the Federal courts, depending on the nature of the spending (e.g. the government isn't allowed to ignore or write off its pre-existing debts).
Discretionary spending can be changed year to year, but good luck cutting Defense significantly. Taking apart the federal budget (washingtonpost.com)
Originally Posted by Andrew Gubb
I don't know about that - what of the absurd subsidies e.g. to corn, meat, etc? In Spain bullfighting is estimated to take up 47€ of each family's yearly tax contribution. This is a sport that 60% of Spanish people either don't support or are against.
I can't make a list of all of these absurd expenses - and lack of transparency in government spending very much assures that - but the scale of it I believe is staggering.