If you like greenery and want a low/no care option, plant lily of the valley. They look nice most of the summer. By fall the leaves brown and it doesn't look so great, but they're nice the majority of the summer.

If you like color and again low/no care, go for impatiens. They are beautiful, with regular water they look spectacular and they like cooler shady areas. I grow them on the north side and they look gorgeous. They won't die until a heavier frost and then you just pull them up.