Trimble SkecthUp 8 is free, powerful and easy to use 3D modeling program. SketchUp 8 has a large model warehouse. Users can upload their models to share with the community or download other user created models. SketchUp is integrated with Google and was used to create many of the 3D models in Google Earth. This the application featured in the post Design a 3D city with SketchUp. There is also a professional version of the program with a extra features which has to be paid for.
Celtx is a free media pre-production tool. It is used for producing and organizing anything from screenplays to comics. Other projects that Celtx can be used to create are films, videos, stageplays, audio plays, documentaries, machinima, games and podcasts.
Links to all items mention in this post will also be in the Resource Links found on the lower portion of the Resources section.