The Internet provides a means for locating ancestors' graves located throughout the world through "Virtual Cemeteries". There are those that allow you to memorialize a loved one through adding obituaries and inscriptions to a "Virtual Cemetery" upon a persons death and others that inventory and publish data on existing cemeteries. The latter are what we as genealogists seek. As the number of sites grows the data obviously becomes fragmented and one needs to visit more than one site. The bottom three sites attempt to do that for you. Listed below are several sites; some are relatively restricted as the Radio Prague site but worth a visit because of the way it is done.
Rootsweb Tombstone Project
Genealogy.com The Virtual Cemetery
Radio Prague's Virtual Cemetery
For more links, try searching www.google.com and enter "Virtual Cemetery" or just cemeteries if you want to find some to visit.