Infragistics 6.3
I downloaded and checked out Infragistics's NetAdvantage 6.3 the other day. If you do a lot of UI work and like to make your apps look good, I definately would suggest you check them out. They support ribbon like Office 2007 and have several cool features like the AppStylist which lets you apply custom styles easily to your apps and formatted tooltips. They're easy to work with also, having a powerful object model.
If you do a lot of web work, they have a whole suite of ajax controls and a good looking grid for Asp.Net.
If anyone uses them, post your cool ideas or styles for look and feel in your apps.