Papervision3D is an open source 3D engine for the Flash platform. They have really pulled out in front of other frameworks and are not only including z axis animation of Flash objects (postcards in space) but have 3D model support and Swift 3D export. Definitely something to watch.
They have a pretty exhaustive list of sites including:
http://www.sprintenterprise.com/burnandbrag/
http://www.nike.com/jumpman23/xx3/
http://www.whitevoid.com/application
http://blog.papervision3d.org/2008/03/05/16-ways-to-organize-information-in-3d/