It's not really flats or offshore, but the amazon river in brazil for peacock bass and other exotic species would be nice too. Some of the species get pretty big too. anywhere from 2 kgs to 200 kgs.
Here is a species list and a exculsive outfitter site. I am not recomending this particular place of business, but just the area. Although this place could be great. Just using this website for the fishing info.
http://www.riverplateanglers.com/ama...species#traira