An exciting online project is found at historicgraves.com. Primarily devoted to gravestones of Ireland and the United Kingdom, the project aims to digitally record and publish historic graveyard surveys and stories. This slideshare presentation tells more about the project:
Once you are at the Historic Graves site, you can do a "family search" under the search tab. You can limit the search by surname, keyword, and by a specific graveyard.
To read even more about the Historic Graves community based project, see:
HistoricGraves 2012: the Project
While I was unable to locate any of my own Irish ancestors at Historic Graves, it was wonderful to be able to see the graves and epitaphs, and learn more about the cemeteries throughout Ireland. I encourage you to take some time exploring this excellent site!