Things I liked about my old chair:
-highly adjustable arms, up/down, forward/back, pivot in/out
-high back: high enough to rest the back of my neck on the top to rest sometimes but not ideal
-curved back (kinda formed to hold you in the center, maybe compare it to something like a car seat)
-bad-ass oversized rubberized wheels that you'd expect to see on a top of the line skateboard rather than on the bottom of a chair. Dead silent on hardwood and one push would take me all the way across the room. Seriously, the wheels are just incredible. When I got my new (piece of shit I'm using now) chair, I noticed that most chair wheels connect to the chair the same way. I was able to use my old wheels but the added height to the chair made the chair too high so that the lowest chair setting was still too high.
Things I'd like to improve:
-better lumbar support
-better tilt/rocking ("synchro tilt" mechanism which tils the back without moving the seat for better comfort)
-better head support. I pass out in my chair a lot so wouldn't mind waking up without a sore neck. Also nice to have neck support while leaning back for watching video, etc.
-adjustable seat bottom (move forward or back for comfort)

I've been looking around the net and above is the version 2 of one of the most popular ergo chairs sold. It runs 745.00. The Version 1 is 607.00
Here's a demo video of the V1 chair: 607.00
http://www.youtube.com/watch?v=I5lbTpB-ktI
v2 chair, less fancy demo:
http://youtu.be/EMjJ0RVnFzQ?hd=1
Concern in that second video is I hear some squeaking. Don't want squeaking!
The biggest difference is the arms which pivot and adjust up/down but done adjust in/out (width) or back/forward like v2.
You also have the option of fabric or leather for the older version. I'm undecided on mesh/fabric/pleather. There's some color options as well on the older version. In fact, beyond the 5 standard colors, you can choose from about 100 fabric patterns if you give them 5 extra days to customize it.
V1:

Differences between v1 and v2:
-more arm adjustments (forward/back and in/out (width)
-5 tilt lock adjustment settings
-narrower seat. some peeps complain that if you have 35+ inch waste, it too narrow so not good for fatties.
-front of seat a little more tapered for better ergo on legs
It's a tough call. I use a mesh chair at work so I think I can deal with mesh. It's cooler solution as well. (less sweaty ass syndrome)
The differences:

Anyone else have a chair they like?