I was just having a chat with my landlord and we got talking about good cathedrals we'd seen. My favourites are:
Hallgrimskirkja in Reykjavik:
(My landlord's were Barcelona and Reims.) I think Hallgrimskirkja is technically not a cathedral but it was impressive enough (and dominated its surroundings enough) to count as one for me.
What are yours? You have to have seen them in real life.