For a tall rider then you would do well to look at a BMW GS, differant engine sizes.
Other bikes that would suit, Honda’s Africa Twin, you need o be 6 foot at least to climb on to it.
The Triumph Tiger is definately 6 foot and over.
KTM Adventure would suit a tall person, I believe their new RC8 would fit the bill too, and it is so sweet, LOOK AT THIS,
Aprilia’s RSV needs a tall person, its not unusually tall, but the riding position tends to favour a taller person.
This might be of interest, however, seat height is not the whole picture, you have to combine it witht eh forward reach and the reach to the footrests.
Any of the large capacity 70’s machines tend to be tall, things like the Laverda Jota or the early Goldwings.
http://www.tallclub.co.uk/reviews/index.asp?category=3&action=view