Blender is the best free and open source 3D modelling program out there by a long shot!
The program is under constant development, has a huge community and has been used in many major films for video editing and 3D concepts. As Said before blender has new builds being uploaded hourly at graphicall.org and you can download all the official stable, aplha and beta versions of the program at belnder.org.
The community is friendly and welcoming and you can fit right in at sites suchs asblenderartist.org, blendernation and blenderguru (great website for tutorials. I myself have been using the program for about six years now, and have used it for both personal and commercial projects: These can be seen at (sixthlaw3d.wordpress.com).
The program has a brilliant set of tools, and the development team are constantly making improvements on the software to keep it cutting edge and competitive. This is a very, very short summary of this awesome program but check out it in more detail in the above links :)
download here: http://www.blender.org/