Official Mystery Books Lists From Known Mystery Writers and Organizations:
Here you will find lists of recommended mystery books. It is a good start into the mystery genre.
I haven't read all the books listed but the lists are written by mystery writers, organizations, book clubs,
readers votes, etc. so they should be a good source. What is more many books appear in almost every
list( ex: The Murder Of Rodger Acroyd") which is a good sign that only the top mystery books are listed.
There are also lists of more recent books if you are interested in that.