What's the movie called with the boy who finds a robot suit and fights aliens with it

Star Kid (http://en.wikipedia.org/wiki/Star_Kid)

Its either Transformers or Iron Giant

Could it be this one? You didn't say if it's animated or what year it was from so maybe this is it:

http://www.imdb.com/title/tt0101988/plotsummary

I think it is Iron Giant too