Al's Orchid in Leesburg, Va in the upper part of the state. killer orchids and also a great display set up by roxrgniess. an eight foot long display. i think there are pictures of the build on this site somewheres.
J&L Orchids is fantastic...I've been there, and their stuff is top notch. Some of their specimen plants are unbelievable!
If you cruise a little west, I also enjoy taking a trip out to Ott's Exotic Plants in Collegeville, PA. They have an indoor rainforest setup, and particular sections of the greenhouses just for tropical plants. They also have a HUGE selection of cacti and succulents, if you like that sort of thing.
Julius Roeher's Nursery in Neptune, NJ (maybe Wall, I forget) is great to look around. They supply botanical gardens, and a lot of their stuff is HUGE. Full-size tropical trees, etc. Last time I was there, my favorites were some great 5' tall tree ferns. Not sure if there will be many terrarium plants there, as it's been 6 or 7 years since I've gone, but if you're passing by, it's worth the stop, just off of the NJ Garden State Parkway. Silva Orchids is also very close by (same exit on the parkway, even), though I've never been there.