According to Official Guinness Records,
The most audio books published for one author is L. Ron Hubbard (USA) with 185 audio books published as of 21st April 2009. As of this date, another 23 of his books were being formatted for release. Most of the works published in this format consisted of pulp fiction and Scientology books.
For a complete list of 2009 records, please visit 2009 Guinness Records in United Kingdom.