I really like FindAGrave.com.
But a few words of caution: The people who have set up the site will tell you that it is not a genealogy site. There are certain people on that website who will quite vigorously protect the main function as a 'graves registration site' irregardless of the fact that caretaker records or obituaries or other 'official' indexes can be wrong or incomplete. Certainly no one wants to be the person who creates inaccurate information, but woe be to the person who actually does. So keep a low profile, and you will stay under the radar of those who thing they are 'helping' the websites operators and administrators.

Also with FindAGrave, there are some people who purposefully place incorrect information that is seemingly meant to mislead. So as always, once info is found, contact a local historical society or the local cemetery.