Currently, the US sits on first place and is spending a few billion more than the next 8 countries combined. Back when it was competing with the Soviet Union, how did the two compare, and how much was the Soviet Union spending in today's money and what part of their budget was allocated for military spending?
The tabulated data I have is for 1970-1971, when the US was still in the process of withdrawing from Vietnam, but an ARPA report [1] on the balance of conventional strength between NATO and the Warsaw Pact includes military budgets for all the member countries. The Soviet military budget was about 40 billion USD, or about 8.1% of GNP, while US military spending was almost 80 billion USD, also about 8.1% of GNP.
Interestingly, Soviet defense spending seems to have been much more efficient than American. Based on US Army firepower measures, a Soviet division had at least two thirds the firepower of an American division, despite the overall division slice (number of soldiers in the army divided by number of divisions) being about a third as big. Assuming the 161 divisions in the Soviet ground forces are maintained (on average) at half strength during peace, this would mean they were supporting the equivalent of at least 53 US divisions' worth of firepower; with twice the overall military budget, the US had about nineteen divisions. Now, this isn't the only way to measure military effectiveness, but it's certainly an interesting comparison to make.
[1] Nato Military Policy: Obtaining Conventional Comparability with the Warsaw Pact, by Steven L. Canby.