Heheh, always make me think of this:
Most asked for feature: 2 way data binding...
Least used feature: 2 way data-binding.
Take a look at knockoutJS http://knockoutjs.com/, It's a bit old (far older than NG) but was used quite widely. They are actually using it where I currently work [sigh.] It is fairly concentrated on the whole two way data-binding thing.