From Ancestry.com on using GNIS for cemetery location and other searches: If you're not lucky enough to have the name of the cemetery on a death certificate or through some other record you have collected, map out the cemeteries that are near where the individual lived. For those searching in the U.S., the U.S. Geological Survey's Geographic Names Information System (GNIS) is a very useful tool (http://geonames.usgs.gov). Click on "Query GNIS" and by entering the county name and state and selecting "cemetery" from the "Feature Class" drop-down menu, you can see a list of cemeteries for a particular county.
From the list of results, you can click on each cemetery name for more information and to map the location using Topozone, TerraServer or Tiger Map Server from the U.S. Census Bureau. Both Topozone and TerraServer DRG are topographical maps that show water features and other geographic features. The TerrasServer DOQ map is actually an aerial photograph of the cemetery. (I'm hoping someday they'll tweak that zoom feature so I can read the headstones too!)
You can also locate some of your ancestors' other "haunts" using this tool, including schools, churches and "populated places." Maps show streams, rivers, ponds, wooded areas, mountains, valleys, etc. If you have an obscure U.S. town or feature name associated with your ancestor, this is a great place to look.