StrategyPage (an awesome military news resource, with no permalinks) posts some numbers that show that although the US spends far more money than any other country on its military, when purchasing power is taken into account the differences shrink (a little).
October 22, 2003: Global defense spending is generally thought to be concentrated in the United States, and a handful of other countries. This is generally true. If you take just money spent on military items, the lineup looks something like this (as a percentage of global defense spending, in year 2000 dollars);The post also points out that good training and leadership are critical to the effectiveness of any military, and I imagine that poor training can cost just as much as good training. Poor leadership can actually cost more than good leadership, depending on how corrupt your leaders are.
United States 43 percent
United Kingdom 5
All Other Nations 38.
However, if you take into account Purchasing Power Parity (or PPP, the relative cost of common goods in different countries), those nations with lower costs (like China and India), loom larger.
United States 31 percent
All Other Nations 62.
Nations that spend little cash, but have cheap local costs (food, housing, payroll), like Iran and Pakistan, all of a sudden have larger defense spending (Iran is now about six percent of U.S. spending, and Pakistan about four percent.)