The Pentax 645 medium format series is renown for low mirror vibration.
Don't forget that shutters cause vibration, too. Leaf shutters generate less vibration than focal plane shutters. On the other hand, some focal plane shutters generate most of their vibration when closing, after the picture is taken. It's also true that in some cameras most of the vibration caused by the mirror occurs when the mirror drops, after the picture is taken.