While you will never see a trillion dollars in person (nature's way of protecting your sanity amidst the bailout), computers can do the job without breaking a sweat—or worrying about retirement.
This particular rendering was made through Google SketchUp, Google's 3D modeling software. Measurements were taken of a $10,000 stack of $100 bills (just half an inch thick!) and pretty much multiplied from there using simple geometry. In that trillion dollar shot, each pallet holds $100 million...and the pallets are double stacked.