What is a good 3D library for Adobe Flex?

I need a 3D library t开发者_JS百科hat works well with Flex... NOT Flex Builder - the free Flex SDK.

Papervision 3D. Note Flex Builder is an IDE that internally uses the Flex SDK (and sort of simplifies life for you). There is nothing that stops you from using any library with Flex SDK (if you know how to add them to your project etc).