A few months ago I threw together a short presentation on the history of calcium imaging for a journal club here at Janelia. It is incomplete. It lacks notes. It is technical. It focuses much attention on early genetically-encoded indicators. However, calcium imaging is so intertwined with the work of Roger Tsien, my Ph.D. thesis advisor, and since he just won the Nobel Prize, I thought it might be of interest to some of the audience of Brain Windows. It does provide a little bit of background for some of the more recent developments chronicled on this site.
Enjoy.
Brain Windows 
Thank you very much for the video of a great lecture on fluorescent proteins by Roger Tsien
For more info on the history of calcium imaging, please see this book chapter.
Tsien, R.Y. 1999. Monitoring Cell Calcium. In Calcium as a Cellular Regulator, ed. by E. Carafoli and C. Klee. New York: Oxford University Press, pp. 28-54.