ComponentArt Atlas Controls
ComponentArt just released a version of their Web.UI suite, which is built for ASP.NET AJAX (aka “Atlas”). Web.UI 2006.2 for ASP.NET AJAX is “the most advanced AJAX framework available. ComponentArt Web.UI for ASP.NET AJAX is the first commercial control suite designed to fully utilize this new framework.”
I haven’t had a chance to do more than view the demos but they look pretty slick. The line between thin and thick clients is really blurring quite a bit now that we’re starting to get some serious client-side APIs for the web, and controls from third parties like ComponentArt do a great job of lowering the bar for how much a developer needs to know to build extremely dynamic AJAX-enabled web applications.