What child seats have a quick-release mechanism? I'm looking to purchase a rear child seat for my almost-two-year-old. 

The main feature I'm interested in is being able to very quickly and easily take it on and off. 

This Yepp Maxi I saw in a store here in NYC fits the description but it is $210+ and that's more than I wanted to spend.  REI link for Yepp Maxi 

What others are out there?
I know this is a late response but others like me might still refer to this page for advice. (I know I did read up on this before we made our decision)

We have just brought a Soosi Flinger bike seat for our 14 month old, 10 kg toddler. He loves sitting in it! It must be comfortable enough as he fell asleep in it during a ride! My husband likes the seat/bracket system because it is quick to take the seat off when he rides his bike to work.

Here is a link to the manufacturer's website: http://soosi.flinger.com.tw/sw-bc07-1.html