Just bought one of these:

http://www.steelcase.com/na/leap_products.aspx?f=11852

...and am very happy with it. As I have the beginnings of lower back pain, I've been searching a couple years for a very good desk chair. In fact, I was ready to drop more than $1000 if need be. I tried all the Herman Miller chairs (e.g. vaunted Aeron), Humanscale Freedom chair and everything in between, but think this is the best...at least for me. It was still $800, but money well-spent I think, considering how much screen time we spend. I know seating is very individualized, but thought I'd share.