One thing I'd like to see added to the ASP.NET AJAX Control Toolkit is the ability to sort table columns. I worked on a project that had this in the past and I really liked it. Granted, ASP.NET has this capability built into a number of controls, but this feature was completely client-side. I may see if I can get a hold of that and create an extender myself, but that will all depend on the time I have and the customer's desire for the capability.