The ASP.NET group at Microsoft released the Atlas Control Toolkit this week. If you’re doing ASP.NET stuff, you’ll want to look at this. They’ve got quite a few built-in Atlas controls. Scott Guthrie sums it up on his blog.
It is the start of what is going to be a very large set of controls that make common Ajax scenarios super easy. Want to add nested drop-downlists to your page? Use the new CascadingDropDownList extender. Want in-line popup support within a page? Use the new PopupControl. Want to implement smooth show/hide support? Use the new Collapsable Panel. Want to add water-marking support to input controls? Use the new TextBoxWaterMark extender. All of these controls can be used on a page without having to write any code or custom JavaScript, and have Visual Web Developer and Visual Studio toolbox and WYSIWYG support built-in.