In terms of total food production, the best numbers I can find (from 2010) show China, India, U.S., European Union 27, then Brazil as being the five largest total food producing nations (in that order).
For wheat: European Union 27, China, India, U.S. and Brazil
For corn: U.S., China, Brazil, European Union 27, and India
For beef: U.S., Brazil, European Union 27, China, and India
For soybeans: U.S., China, Brazil, European Union 27, and India
For pork: U.S., China, European Union 27, Brazil, and India
For rice: China, India, U.S., European Union 27, and Brazil