Last spring I got a free packet of seeds with a gardening magazine -
Rudbeckia Rustic Dwarfs. They began flowering in September and the darn
things are still in flower (but struggling now), even after some very severe
frosts and a heavy snowfall. I even pulled some up to make room for bulbs,
but I just left the clumps on top of the soil, and even these are still
going strong! I thought they were annuals but they must be perennial.

Highly recommended for those with not-so-green-thumbs!