For about ten years I have used a Herman Miller Aeron Chair. Expensive but VERY good. You have to try one on for size (3 sizes; Small, Medium, and Large; I have the large one). Highly recommended.
It was more than $100 cheaper at Office Depot. In addition, they offered a 20 percent coupon. My wife needs a good chair. She is on her computer all day. For me, all I want to do is for the Winter to end, get back on my bicycle, and enjoy my repaired heart.
I have to second the Herman Miller Aeron Chair. Almost 2 years ago, I began working from home and I had a cheap(er) $200 chair. I have never had back problems before and I began having back and leg problems sitting in it all day.
I thought that I would spend around $500. There were many reviews in all of the chairs in that range that said they were good, but they weren't a Herman Miller.
After the sticker shock wore off, I tried one out and I wasn't impressed to be honest. I got one anyway, with lumbar support, because I have never seen a bad review.
Within days, my back and legs stopped hurting. There has not been a day of pain since I got the Herman Miller. It is sooo worth the price.