I don't -memorize- Latin names exactly, but I go to plant places often. I think the National Arboretum is the place I miss most in the DC area. They have a great magnolia/ holly area that doesn't seem to be in the site tours. :^/ The Botanic Gardens by Congress is also great- giant greenhouse, cactus room, etc. And locally, I had to get a Japanese Gardens membership, although that's more about the whole feel of the scenery than just the plants. (Also, the rose gardens are just down the hill.)
http://www.usna.usda.gov/
http://www.usna.usda.gov/Gardens/collections/VirtualTours/index.html
http://www.usbg.gov/
http://www.usbg.gov/virtual-tour/index.cfm
http://www.japanesegarden.com/