I was only 5 years old in '80, so I really don't recall the hockey game at all. Here are my biggest 'dogs that I remember (approximately mid-80's) to now:
1. Tyson-Douglas: as noted previously.
2. The 1988 Dodgers: beat two supposed super-powers on the way to the World Title. The Mets & A's had tremendous star power: McGwire, Canseco, Strawberry, Cone, Gooden, Stewart, Eckersley, etc. .. but the Dodgers took them both down (A's barely got to 5 games) with a line-up of Steve Sax, Franklin Stubbs, Mickey Hatcher (as the 3 hitter!!), Mike Marshall, John Shelby, Mike Scioscia, Jeff Hamilton, & Alfredo Griffin .. remember, Kirk Gibson only had one AB in the WS. This doesn't get enough pub for being the enormous upset that it was.
3. 1991 Duke over UNLV. No one gave anyone a chance against the Rebels that year, much less Duke who was absolutely throttled in the championship game the year before.