I'm not a Krugman apologist, and can't bear to read his NYT columns, but he does actually have academic credibility ( even though it is from work he did a fair while ago).

This is a good analysis of Krugman's contributions to international trade from when he won the John Bates Clark medal in 1991 - http://web.mit.edu/krugman/www/dixit.html. I'm not sure he's done anything too groundbreaking since then.

He's also co-written the textbook most undergraduate economists use (including me) for international trade - http://www.amazon.com/International-Economics-Theory-Policy-...