Petunia
Size: 8 inches to 2 or so feet
Lighting requirements: Full to part sun
Seasonal interest: Spring through frost blooms
Winter: Dies in the winter
There are quite a few varieties of petunias out there. I like the newer 'Wave' Petunias.
It seems that most of them tend to get leggy by mid summer and slow down on blooming. I may have just picked up varieties that struggled, not sure. I'll try a few different ones soon and report back.
I much prefer Petunia's cousin Calibrachoa (Million Bells). It was fairly recently recognized as a separate genus that just behaves a lot like Petunias.