The greatest contribution to science is the invention of the harnessing of electricity. I chose this invention because it led to so many others. Modern life would not be possible without electricity, and almost every other important invention requires it.
Edward Jenner developed the process of vaccination. I think this and other medical advances have to rate very highly on the scientific accomplishment list because they actually alleviate human suffering. Many other advances are twisted to cause human suffering.
The most important part of science is reporting the results and the organizations, which report the results. With that in mind, I think that King Charles II made the greatest contribution the reporting of results when he chartered the Royal Society in 1660.