Just 2 days ago i watched a TED Talk by Niels Diffrient: Rethinking the way we sit down.
"Design legend Niels Diffrient talks about his life in industrial design (and the reason he became a designer instead of a jet pilot). He details his quest to completely rethink the office chair starting from one fundamental data set: the human body."
i liked it better than the humanscale freedom, but ymmv. the liberty is beautifully designed - it uses your own bodyweight to ensure good posture.
drove 1h both ways across LA to sit it in before i bought one online for 1/2 the price that it was selling in the showroom ($700 vs $1400).
it was an awesome purchase - i could sit in it all day. i sold it to go digital nomad for a while, but when i pick a place to live, it'll be one of the first things i buy. jason calacanis' "cheap tables, expensive chairs" advice is bang-on imho: http://tr.im/k490
looks like the liberty has come down in price too: http://tr.im/k48A
Its the Freedom Task Chair by Humanscale. http://www.humanscale.com/products/freedom_index.cfm
I think they are better than Aerons; not sure about the price though.