Having a quick look at BoxOfficeMojo you can see a nice comparison page for the Domestic (US) takings of Transformers, Iron Man and Transformers: Revenge of the Fallen. A basic summary breaks down as follows
US Domestic earnings
Transformers: $319,246,193
Iron Man: $318,412,101
Transformers: Revenge of the Fallen: $268,700,00
Worldwide Takings
Transformers: $708,252,592
Iron Man: $585,133,287
Transformers: Revenge of the Fallen: $508,915,819
Interestingly Transformers: Revenge of the Fallen has now taken 68 million dollars more (in the US) then it's cost to make, and is only $85million dollars behind Iron Man's worldwide total takings. (Obviously there has probably been an increase in box office pricing since the previous two films).
Transformers Revenge of the Fallen is already the 38th highest grossing film in the US and 66th worldwide.