Shp2kml is a stand alone tool that transforms GIS layers to Google Earth. It uses as input the most common format file for GIS (ESRI shapefile) and generates a KML File.
Google Earth requires coordinates to be in Lat/Lon and referenced to the WGS84 datum. Shp2kml is able to transform the coordinate system. The input file can be Lat/Lon (Geographic) or UTM (Projected) coordinate system. Also shp2kml will change datums if required. It contains a list of around 200 datums.
Some of the supported features are:
Lat/Long or UTM (meters)
Point, Lines, Polygons
Symbol properties: by Single Symbol, Unique value, Graduate Value
Labeling from attributes table
Balloon creation from attributes table
shp2kml is a freeware tool. This program doesn't need to be installed, just unzip it and run it.
shp2kml.zip contains the executable file (shp2kml.exe)