Previously on HN:

http://news.ycombinator.com/item?id=585693

Ergohuman is the closest I can find to the Aeron, but I haven't tried one yet. They're also pretty close to Aeron in price, around $600:

http://ergohuman.com/index.html

Realspace Pro 9000 is close too:

http://www.officedepot.com/a/products/690690/Realspace-PRO-9...

A Slate article looking for the 'best desk chair':

http://www.slate.com/id/2131646/

Some others worth looking at:

Herman Miller Ecua XR:

http://www.costco.com/Browse/ProductGroup.aspx?Prodid=113004...

Humanscale Liberty:

http://www.thehumansolution.com/liberty.html

Hayworth Zody:

http://www.geek.com/articles/gadgets/review-haworth-zody-cha...

Realspace BT2:

http://www.officedepot.com/a/products/392830/Realspace-BT2-B... (I randomly found this one in Office Depot recently, and liked how it felt so much I bookmarked its page. I'm not Big & Tall, just average, but this chair's posture & lumbar support felt great)

Here's a fake Aeron:

http://www.coolchairz.com/solid-metal-mesh-chair--metallic-t...

Lots more at http://www.ergodepot.com/

Even a TED Talk on sitting:

http://www.ted.com/index.php/talks/niels_diffrient_rethinks_...