Mammoth Grey Stripes Sunflowers have huge blooms, that grow to be 12" across, sit atop stems that grow to be 8'v- 12' tall.
 
Extremely fun to watch grow, their massive seed heads are good for harvesting and roasting or leaving in place to feed birds.
 
These do best in full sun. Though sunflowers are not finicky, they do appreciate loose, well-draining soil. Choose a location that is sheltered from strong winds, perhaps along a fence or near a building. Also consider the height that the particular variety will reach.