favorites: Castor Bean Plant
Last year was the first time we grew this plant, and it grew to an impressive, majestic 10 feet tall. This year, my small effort at starting seeds failed, and it was late in the season before I found a seedling to buy. It wound up in the shadow of something more established, and never got more than 2 feet tall. Still, I'm enjoying its red red foliage, before the frost kills it off.
Third photo: last years plant. Heck, maybe it was even a different variety.
Click here to go to more info on this (all parts are toxic!) plant.