This month (february) I have been working really hard on a clients project creating a ajax enabled website, and the hard part is not how to get it working the way I want but rather to create some nice looking (and reusable) extender controls from my javascript behaviours.
I have published a free extender control available for download - and the purpose of it is to ease parent/child checkboxes - you know "Select/Deselect all". The Checkbox extender control lets you also define an associated label - so that when all child checkboxes are selected the label for the parent switches to "Deselect all" - or whatever (user defined).
I have turned to the Ajax Control Toolkit to aid my control crafting, usually I don't like adding ANY dependency at all to my controls making deployment as easy and small as possible but honestly - this one looks worth it full 1 MB.
Please download - but first - don't miss the demo