First, it's against our rules to include countries just because of the great variety of ethnic food available. Canada, Australia, and the U.S. are obvious examples of that.
A short Lonely Planet article offers up its list of ten great food countries here.
We've been to all of them except India (well, we've eaten lunch in Malaysia, although haven't visited Indonesia). We'd definitely substitute Singapore for Japan on that top-ten list - even though we love udon noodles, sushi, and tempura.
Part of Singapore's attraction is the variety of cuisines available, but there's a definite Singaporean cuisine, and that tiny nation deserves a place on any list of "best" countries for food.
We'd write about this some more but we're too hungry.