This image shows military spending as percentage of GDP, which might be helpful. It shows that the US is roughly in the same area as Russia, Colombia, Uzbekistan, Greece, Egypt or Algeria, while being exceeded by countries like Turkey, Saudi Arabia, Syria and Mauretania.
One might note though, that the US does not face any credible threat to it's mainland. Large part of the US military budget goes into developing extremely expensive aircraft like the F-22 or the JSF, which are useless against the most significant threats faced by the USA today: Information Warfair and low-intensity asymetric conflits.
Another huge part of the budget are the carrier groups the US maintains to retain dominance of global trade routes. Internationaly, most carriers are now likely to be obsolete as anti-ship missles and diesel-electric subs can easily take them out. The highly sophisticated nature of the US carrier groups (AEGIS + accompanying sub) means that the US aircraft carriers might still be able to establish control over the most important sea-lanes in case of major war. However, the balance can easily tip against them, and the opposing systems are far cheaper and easier to use.