One things they had was a ginormous zircon crystal on a big rotating disc. The crystal would go around in a circle every 5 seconds or so. At the bottom is a geiger counter, so as the crystal got closer and closer, the geiger counter started registering more and more counts. I took a series of pictures hoping you could see the meter on the counter and the position of the zircon, but alas, not enough light.
But perhaps my favorite part was a short video entitled "The Clocks in the Rocks" (see the transcript here). The story has two characters, a woman who is the geochronologist, and the guy who wants to know more about geochronology. They are in a TIMS lab (thermal ionization mass spectrometry), and the video goes through the basic steps of getting an age. Unfortunately none of my pictures of the TIMS filament or the ion-exchange chemistry came out, but you get the point.
What I liked most about this video was that even though it was simplified and directed at a general audience, it wasn't dumbed down or incorrect. I think this is key to attracting young students into the geosciences, the discipline has to be presented as rigorous, as something more than mineral collecting. It is easy in the earth sciences to fall back on pretty pictures and catastrophic events as ways to hook students, but that tends to misrepresent what professional geologists actually do.
Anyways, the rock sample they allegedly used for this video was from Half-Dome, and in the end they show a concordant U-Pb age of ~86 Ma (on a Wetherill Diagram).
So two thumbs way up for the Smithsonian Natural History Museum Rocks and Minerals display. Unfortunately I did most of my museum visiting when I was young, and this is one of the first times I've gone to a place like this as a professional geologist. I'd be interested in reviews of other public museums and how well/poorly they treat geology.