A dollar bill is approximately 0.0035″ thick. So, a stack of one billion dollar bills would be 55.24 miles high.
A stack of 224 billion dollar bills (the approximate cost so far of invading Iraq) would be 12,373.76 miles high. That’s halfway around the earth’s equator (the earth’s circumference is 24,900 miles).
A stack of nine trillion dollar bills (the current US debt ceiling) would be 497,159 miles high. That’s twice the distance from the Earth to the Moon.