The below information is outdated.The St. Louis City Public Library website offers two ways to search indexes of obituaries from the St. Louis Post Dispatch.
Please follow this link for more recent info.
The St. Louis Post Dispatch Obituary Index has annual indexes for 1880-1927, 1942-1945, and 1992-March of 2006. They have stopped updating this page, and it isn't linked to from their main site, so it can only be found via old links to it. (Or new ones like the one I just made.)
There is also the Obituary Search database which currently has data from: 1880-1930, 1942-1945, 1960-1963, and 1992-1997. This doesn't contain the more recent years, however, since the Post Dispatch archives allow you to search back to 1988, that's not a big deal. The older years are more important.
The database now has all the pre-1988 data the old index had, with some additional years. However, there are advantages to the index. The biggest advantage is that it gets indexed by Google, so you don't always need to know about the index in order to find the information. With the index it is also easier to locate misspelled names.
The database has some flexibility.
You can search on fragments of names, so if I enter "New" in the name field, and a year such as 1945, I receive 24 suggestions which include my great uncle Mandell Newmark, but 23 other individuals whose last name begins with "New".
A search on: Mel N (without any year) yields 65 results, including my grandfather Melvin Newmark. However, I can't differentiate between first and last name, and the database limits results to 100, so a search for: 'Ben C' doesn't yield my great grandmother's brother, Ben Cruvant. There are way too many last names beginning with 'Ben' for the database to reach the Cs. A search for "Ben Cr" works though.
What do you do once you find the date of the obituary you want?
Post Dispatch Archives
You can purchase the Post Dispatch archived articles for $2.95, and get the text of the obituary that way, or you can write down the date and look them up in the same fashion as below.
St. Louis Public Library Index or Database
If you do live in St. Louis, you can find the obituary in the microfilm archives at either the St. Louis County or St. Louis City headquarter libraries.
You can also request the County library photocopy and mail it to you. The fee is minimal.