San Francisco, CA. The artifacts are incredible, but I couldn't help admiring the vitrines as well, in "Teotihuacan, City of Water, City of Fire" at the De Young Museum. The pedestals are stepped at the bottom giving them extra weight and presence, like the architecture the artifacts would feel at home in.
Even where a base might not be neccessary, the pedestal adds something to the presentation.
Freestanding vitrines have various stepped pedestals set inside a full sized plex box.
So the plex seems to float, giving the artifacts breathing room.