VTK and ParaView (Score 1)

Look into VTK and ParaView. Both open source packages (BSD license) from kitware (vtk.org and paraview.org). Historically they have been a scientific visualization system, but in the recent two years they have worked with Sandia Nat'l Labs to add an extensive information visualization subsystem. They major goal of the work is to make it scalable (using distributed parallel processing); something that's really important as data sets get large.