Depends what you want - there are tall varieties, dwarf ones, yellow ones, red ones, bronzy ones, double ones, single ones, ones with huge heads, ones with loads of small heads.........what do you want? Any garden centre will have a selection of varieties, or have a look on e-bay.

If you're thinking of cut flowers, look for pollen free varieties: much cleaner and easy on the allergies.

tall ones

Hi Charlotte - welcome to GoY! I've done some research and the tallest variety I can find is an F1 hybrid called 'Kong' and that is said to grow 3-4 metres!! To grow a really tall sunflower, you'll need to enrich the soil with lots of good stuff like well rotted manure and bone meal and grow it near a wall so that the plant stretches up towards the light to some extent (not full shade tho). Good luck with it! BTW Kong is available on e-bay for 99p.