OpenDX - "As its name implies, OpenDX is Open Source. The license allows you to freely create, distribute, and develop visualization solutions as you see fit.
OpenDX is a uniquely powerful, full-featured software package for the visualization of scientific, engineering and analytical data: Its open system design is built on a standard interface environments. And its sophisticated data model provides users with great flexibility in creating visualizations...The GUI is built on the standard interface environment: OSF/Motif(tm) and X Window System(tm). The current version supports software-rendered images on 8-, 12-, 16-, 24-, and 32-bit windows." Supports Windows, Linux, Solaris, OS X and others. A Java version is planned. The gallery of animations is pretty cool.