Scott Guthrie, the General Manager of the .NET Developer Platform team, has a fantastic video up on the ASP.NET website that demos some of the cool features in the ASP.NET AJAX toolset, formerly known as Atlas. At the risk of sounding sycophantic, I think that Atlas is one of the coolest products in development at Microsoft today. One of the things I hate the most about developing asynchronous web applications is the horrendous state of the tooling. Atlas gives you the ability to develop Ajax apps with all of the normal VS 2005 tooling around it. Pretty cool stuff.
In any case, the video linked to above shows Scott creating an asynchronous to-do application with a backend in 20 minutes. Well worth watching.
[This message was pre-recorded; Aaron is currently on vacation]