ProViz is a program visualization framework for Java. It is built as a plugin to the Eclipse IDE. (We are getting close to publishing resources and making this project distributable. Stay tuned!) A video demo: http://www.youtube.com/watch?v=BsoK1n-OM
Theba is a plugin-based image analysis framework for segmentation of and measurements on 3D and 2D images. Theba has a nice GUI that allows inspection and manipulation of the image and a wide range of plugins including segmentation.