This looks really cool: http://p068.ezboard.com/fhirstartspostyourownpictureshere.showMessage?topicID=1739.topic. Modular 3D dungeon tiles to lay out a dungeon as you move through it with miniatures...
Hirst Arts (http://www.hirstarts.com/) sells molds and provides advice on just how to do this.
Or one could go the much cheaper route: print out and glue together the tiles found here: http://www.enworld.org/CrookedStaffProductions/page8.html. For instance (there are a bunch of other ones, too):
(http://www.enworld.org/CrookedStaffProductions/plans2.jpg)
Also useful (and that's why I'm posting it here): A PDF of 1/4" Isometric Mapping Paper (http://www.castlemolds.com/plans/isograph.pdf).
Paper = easier and cheaper to store.. The other setup looks like the Druids Heroscape collection.
I completely agree that paper's easier. It also allows the DM to put together sections, like corridors or rooms, and just plop 'em down as the characters can see them.