Oracle JDeveloper ... you can get it for free (for now) from oracle,my modest experience:
1. facesIDE - doc says that it should show u the preview. i can see preview only when making very basic pages:/
2. m7 nitroX - only jsp editor is free. it simply shows rectangles representing your tags (also jsf tags). with somme imagination u can see layouts;)))
it does rectangles over the myfaces components, this at least gives a headstart, besides that JDeveloper is a really nice enterprise IDE.
