Kudos to the Missouri State Archives for the Missouri Death Certificate Project they have undertaken. They have indexed the death certificates for the years 1910 - 1956, and that index is available online via the Secretary of State's website. Even better, they are in the process of adding digital images as well. Images are available (free! in .pdf format) for 1910 - 1930, and 1950 - 1956. They must have quite a team of people working on this, because I've been amazed at how quickly they have been uploading the images.
There is so much valuable information available on death certificates. I'm proud of Missouri for making this information available, at a time when so many other states are reducing the access that we have to such records.
You can access the Missouri Death Certificates database here.