ParaView

ParaView is an open source [parallel] visualization application from Kitware that I have used for many different projects. It offers a quick way to visualize scientific datasets. I also played a small role in helping extend it to perform information visualization, primarily to visualize [large] graphs using the Parallel Boost Graph library (now part of Boost proper).

Snapshot of some data from CompuCell3D being visualized in ParaView.