3D is a big deal in RIA circles. I'm not sure anyone has figured out how to do usable 3D experiences, but there are a lot of people trying and adding some depth to the interactive parts of your applications is getting more and more popular. Swift 3D, one of the biggest names in 3D has a new version of their tool which is targeted at people who want to use the third party 3D engine in Flash, Papervision 3D.
The new tool makes it much easier to take 3D assets and bring them into your rich Internet application. It also has an interface that lets you create and manipulate your own 3D objects. For would-be-3D designers or anyone who wants to experiment with 3D UI paradigms, Swift 3D is an excellent tool. Lowering the barrier to 3D is an important aspect of getting better at using 3D in interfaces. For the most part I think that 3D is associated with the more gratuitous side of UI but it won't always be that way.
Having support for Papervision means that there is finally a great tool to take advantage of that framework. Electric Rain, the company behind Swift 3D is also doing a lot of work with WPF and Blend. They have ZAM 3D which provides the same set of functionality on the Microsoft RIA stack. This is a cool company and because they straddle both products, they can enhance the 3D experience across the entire RIA spectrum. It's available on both Mac and Windows.