I'm interested in what y'all think the “best” and coolest new features of ASP.NET 2.0 are. By “best” I mean, what feature will allow you to best get your work done; by coolest I mean what feature blows people's socks off. And let's stick to just ASP.NET 2.0 features, leaving Visual Studio 2005 features for another entry.
For me, I'm not sure what the best feature would be yet, I've not used 2.0 to create any real-world applications. My hunch is that the provider model is going to be high on the list (at least initially), allowing me to more easily move over existing applications with existing membership, role, profile, and site navigation solutions to take advantage of 2.0's new Web controls.
For the coolest feature, the one thing that always seems to impress my students the most is the GridView's built-in capabilities coupled with the ease of data access from the SqlDataSource. Being able to go from a blank page to a pageable, bi-direction sortable, editable, deletable interface in about 35 seconds leaves many jaws on the floor the first time it's demoed. Granted, creating real-world apps involves more than 35 seconds since they shouldn't be using SqlDataSource controls and should include various validation and other business rules for editing and deleting, but the demo still does get 'em every time! :-) (There are plenty of other “cool” things about ASP.NET 2.0, but I think the fact that this one can be done quickly, results in pretty pictures and easy to see highlights, and basically takes a task that takes 35 minutes in ASP.NET 1.x is what drops the jaws.)