I watched some bad classic fantasy movies a while back - Krull and Dragonslayer - they were pretty fun. I remember watching an old one on TV called the Ice Pirates years ago that was pretty good too.

Excalibur is a good one but it's maybe more on the side of good than so-bad-it's-good. It's darker whereas the other ones are weirder/random.

Oh, and everyone owes it to themselves to watch the Ewok movies Caravan of Courage and Battle for Endor.