You can find tables (not graphs) of the US National Budget allocations since the 1940's in a single PDF:
http://www.whitehouse.gov/omb/budget/fy2006/pdf/hist.pdf
If you have your heart set on looking graphs, you can find several from the website for the US House of Representatives Budget Committee:
http://www.house.gov/budget/chartsgraphs.htm
You can also see various budget, deficit and spending statistics, some graphed over time, on the Public Agenda website:
http://www.publicagenda.org/issues/factfiles.cfm?issue_type=federal_budget
And if you want to really veg-out with numbers, try the Financial Management Service's website (they're a part of the US Treasury Department). They provide reports (in PDF and XLS files) on the receipts, outlays and balances of the US Federal Government. I particularly like the reports on this page:
http://fms.treas.gov/annualreport/index.html
Hope this helps!