Actually; it's USA, China, UK, France, Russia, in that order.
This is based on expenditure for 2011, man power, budget, population and GDP, among others, by the way.
USA:
Government type: Constitution-based federal republic
GDP: $14.12 trillion
Military Budget: $661 Billion
Total Population: 311,000,000
Total Military Manpower Available: 145,000,000
Air Based Units: 18,200
Land Based Units: 30,000
Sea Units: 1,600
Operational Nuclear Weapons: 2,500
China:
Government type: Communist state
GDP: $8.818 trillion
Military Budget: $100 Billion
Total Population: 1,350,000,000
Total Military Manpower Available: 730,000,000
Air Based Units: 2,000
Land Based Units: 32,000
Sea Units: 800
Operational Nuclear Weapons: 180
UK:
Government type: Constitutional monarchy / Commonwealth realm
GDP: $2.123 trillion
Military Budget: $69 Billion
Total Population: 61,000,000
Total Military Manpower Available: 29,000,000
Air Based Units: 1,900
Land Based Units: 5,200
Sea Units: 150
Operational Nuclear Weapons: 170
France:
Government type: Republic
GDP: $2.094 trillion
Military Budget: $67.3 Billion
Total Population: 64,000,000
Total Military Manpower Available: 29,000,000
Air Based Units: 1,000
Land Based Units: 8,500
Sea Units: 145
Operational Nuclear Weapons: 300
Russia:
Government type: Federation
$2.116 trillion
Military Budget: $53.1 Billion
Total Population: 140,000,000
Total Military Manpower Available: 74,000,000
Air Based Units: 4,000
Land Based Units: 80,000
Sea Units: 500
Operational Nuclear Weapons: 4,600
The top 15:
