Keep in mind that no plant will live on total neglect. Potted plants require watering more often than those in the ground because the pots heat up. Plastic pots will retain moisture better than terra cotta, but I prefer the look of terra cotta pots. Glazed terra cotta retain moisture better than unglazed, but not as well as plastic. Be aware that black pots will really heat up and might not be such a good choice on a hot balcony. Bigger pots retain more water for longer than smaller pots (an obvious but often overlooked consideration).

Gaura is also a nice plant for pots, as are ornamental grasses.