White Flower Farm, GRDN Pitch: "I live in an apartment building surrounded by single-family brownstones, and this deck is framed by their enormous, gorgeous backyards. There are lush trees overhead, so I've gone with partial shade to shade plants. ..." [more below]
My favorites are the Geranium Rozanne, a fairly hardy perennial with blue-purple flowers (it's just to the viewer's left of the lounge chair, but it hasn't started blooming yet), and my oak-leaf hydrangea which is very young and not too visible.
If you look closely, it's behind the blue table. If you can't have an oak tree, it's very very nice to at least get the leaves! Both are from White Flower Farm. I've had a lot of success ordering their plants by mail. I also, of course, love a good trip to GRDN, which is just a few streets away.