That's funny... I thought 3D was already huge in Flash. It is really cool though.
I've used Away3D and Papervision3D, but there are others as well. Check out Alternativa3D. Although I haven't used it myself yet, I've read that one uses the native 3D available in Flash Player 10 and that it runs very nicely. I've seen that it looks really good at least.
"Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime." -- Chinese Proverb.