Counting warheads
Two researchers associated with the Bulletin of the Atomic Scientists have published their research on the number of nuclear warheads possessed by countries worldwide, together with data on where they have been deployed based on various sources. The best part is their paper is available for free, and from the looks of it many of the sources the authors draw on to discuss nuclear proliferation seem to be publicly available, too. I plotted the salient numbers here. For the full paper, go here.