I mention the Herman Miller Aeron quite often because, well, it's what I've got. There certainly are other ergonomic office chairs out there, though. Here's a few I scrounged from around the Web:
The Trendway TF series chairs are high-backed with a curved dual-compound seat and adjustable height. I don't like that the arm rests don't seem to be adjustable, and it's not clear whether the back has a tilt option, but the TF series has a range of seat sizes with five arm choices available, so you may find something that fits just right.
http://www.trendway.com/ (look under "managerial task seating")
When I saw the Knoll Chadwick Chair, I thought it looked awfully similar to the Herman Miller Aeron, and then I found out Don Chadwich was the designer of the Aeron and the Equa I (haven't seen that one). The Chadwick Chair is his newest project. It has active suspension and resilient support via the "elastometric" back and seat fabric. It comes with variable seat depths, flexing arm pads, forward tilt, and lumbar support. The frame is black glass-filled nylon with a breathable 100% polyester fabric available in beige, silver, brown, green, and black. Hm, I think this one goes on my Christmas wish list. It seems to have everything you could want in an ergonomic computer chair.
The Kimball Office Wish Task Chair sports a synchronized-tilt recline, multiposition back lock, five-zone tilt tension, and pneumatic height adjustment so users can easily customize the chair to get just the right fit.
I haven't actually tried any of these chairs (maybe some day!) and a lot of the blurbs are summaries of the manufacturers' own descriptions, so you'll want to do some more research if you're thinking about buying any of them. I'd love to hear comments from anyone who has tried any of these chairs.
(Pictures came from the product section of InteriorDesign.Net)