I agree Amid. They probably are the most overused plants, but there's a reason. Easy to grow, flower all summer and your yard always looks great when you put in lots of impatiens.
They may be overused but this gardener likes impatients.
I think for perennials, its definately hostas. They're everywhere....sun, shade, wherever. For annuals, either impatiens or marigolds...enough with the marigolds!!!!!
Impatiens here too Amid, but ditto what Mamu said, they work! Lots of people seem to grow Dusty Millar in the summer, every second house has some. I've never used it.