I did lots of chair research before I replaced mine about a year ago.

The costco chairs are pretty nice, but they are really just a better looking version of your standard office depot chair. They'll only be comfortable for a year or less.

Personally, I think a business grade task chair is the best bet. They are comfortable, last forever, and look sharp. Check out Steelcase, Humanscale, or Haworth... Maybe even a Herman Miller Aeron -- it's what I went with, but I'm a sucker for the plastic lawn chair look. Unfortunately you'll spend 4x more on these than your typical costco/office depot chair, but how can you put a $ figure on comfort, really.