Go to:
www.familysearch.com
and you can access many of the iom christening and marriage records by typing in a name and choosing IGI/British Isles from the sources column on the right.
Then you can refine your search by selecting country (Isle of man), event (christening/marriage), dates, spouse's or parent's name, etc.
Some of the records are transcriptions from parish records, others are LDS member submissions taken from other sources and should be treated with extreme caution.
Frances Coakley has written a number of posts on the subject, most recently on December 14, and in greater detail on 17 October 2001.