Blender – 3D Modeling, Rendering, Animation, Video
Blender is the free open source 3D content creation suite, available for all major operating systems under the GNU General Public License. Its interface is tough to learn at first. But, after some hours with video tutorial instruction or books it becomes a very valuable asset to your personal production pipeline.

Audacity – Simple Audio Editing & FX
Audacity is free, open source software for recording and editing sounds. It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems. It is simple and easy to learn. Just be sure you get the LAME encoder for making MP3′s.

GIMP – The Photo Shop Of The Open Source World
GIMP is the leading photo editor in the open source world. It works like other (proprietary) raster editors including Adobe Photoshop, Jasc Paintshop Pro and Microsoft Paint. You can learn more about the software and even download a copy at http://gimp.org.