I've done a set (Thoumont's Rare Tomes and Components) for WorldWorks, so I am completely biased, but these guys are the nicest bunch you could possibly meet, and they churn out abslutely top quality work. If you're looking for downloadable 3D cardstock scenery, go no further.
Would you recommend printing these on cardstock and gluing them to foamcore with super 77 (or something similar)? to make them more stable. I know that my 4 and 5 year olds will get into them so I want to make them a bit more stable. I do know they have some of the best looking stuff available but don't want to make them a dozen times.