Giant Sunflower Variety
Ripley's Believe It or Not - Giant Sunflower
Height: 14 ft. or more
Head Type: Single-headed
Head Diameter: NA
Days to Maturity: 95-120 days
Description:  Special giant grey striped variety that easily grows 14 ft. or more.

Where can I find this variety?
UPDATE: As of spring 2005, this variety has been discontinued. 
DeerBusters
MasterGardening.com
Personal Experience:
year: 2004
  This is the first year I tried Ripley's Giant Single.  Most of my plants ended up about 12+ feet tall.  I was unable to get any of my plants to get 14 feet or more as indicated on the package.  A few prematurely flowered, and didn't even reach 8 feet, but they weren't the only variety that had that problem.  Plants had very large leaves and stems.  Overall, the plants were pretty impressive.  I plan on trying them again next year. 
Package cover isof the 1976 world record 23 ft. 6 ½ in.  tall sunflower grown by Frank Killand  of Exeter, England  in 1976.
On my  left is a 12 foot Ripley's Believe It or Not - Giant Sunflower.   on my right is a 14 foot Bott's Strain sunflower.   Picture taken on 7/30/04 in New Jersey.