It do IT for a living, so I end up in a chair for extended periods. I spent a bit and a got a chair that is for Big/Tall people (which means it can handle more weight and is designed to last longer, but costs a bit more).
I got this chair:
Realspace Endsleigh Executive Big Tall Bonded Leather Chair ChromeEspresso by Office Depot & OfficeMax
(I got the one in black).
EXTREMELY comfortable. I have had a lot of office chairs over the years, and this is by far the best and most comfortable chair that I have owned. But at $320USD, it is not cheap. (Worth every cent, in my opinion).