Leland Meitzler is back at GenealogyBlog, and today he wrote a nice post about The Missouri Death Certificates Online Index & Digital Death Certificates 1910-1957. Check it out! It's always nice to find another free resource.
I would like to add that you can find many Georgia death certificates online, as well. Georgia's Virtual Vault contains Georgia Death Certificates, 1919-1927. The website copy states, "The collection also includes a number of certificates from 1914-1918, with the bulk dating from 1917 and 1918."