Batch convert GeoTIFF's to KMZ files
Recent versions of gdal_translate have support for KML Superoverlay. Although it is not yet documented on the GDAL website the following can be used:
gdal_translate.exe -of KMLSUPEROVERLAY c:\in.tif c:\out.kmz -co FORMAT=JPEG
This will save a tiled version in a kmz file using jpeg compression.
On windows you can automate using
forfiles /m *.tif /c "cmd /c gdal_translate.exe -of KMLSUPEROVERLAY @FILE @FNAME.kmz -co FORMAT=JPEG"
This assumes that the input files are in WGS84.