PZL M-15 `BelphegorŽ
What an interesting aircraft, ralphos. It does rather fuzzy up the line between "form follows function" and "sheer f**k ugly". A quick Wikipedia scan indicates it was the Russian clients who were looking for a more effective ag plane than the AN2 and who insisted the new aircraft be jet powered. There must be a story there: the early 1970s bureaucracy specifying a design based on the wishful thinking that a jet powerplant would emerge with the instant response of a piston engine.
One wonders what the Poles would have come up with if left to their own devices. I'm sure it wouldn't have been a jet.
My own vote for, if not the ugliest, the most ungainly of modern aircraft, is the Beech 1900 with all its added airfoils.