Houseplants of all types are probably your best bet. Philodendron and pothos would be an easy place to start. You could try putting out some tomato starts for people who want to grow tomatoes in containers on balconies or fire escapes. Once you're out there, you can ask people what else they'd like to see.

I wouldn't worry too much about agriculture inspectors swooping down on your building in Queens. But set up your table so that it doesn't completely block pedestrian traffic, and be prepared to pack up if a cop hassles you about peddling without a permit. If that happens, you may want to find a community garden and pool your resources for a plant sale. Joining a community garden would be a great way for you to do some outdoor gardening, too.