All Windows ContextMenuHandlers (if you want to clean)

HKEY_CLASSES_ROOT\*\shell
HKEY_CLASSES_ROOT\*\shellex\ContextMenuHandlers
HKEY_CLASSES_ROOT\AllFileSystemObjects\ShellEx
HKEY_CLASSES_ROOT\AllFileSystemObjects\ShellEx\ContextMenuHandlers
HKEY_CLASSES_ROOT\Directory\shell
HKEY_CLASSES_ROOT\Directory\shellex\ContextMenuHandlers
HKEY_CLASSES_ROOT\Directory\Background\shell
HKEY_CLASSES_ROOT\Directory\Background\shellex\ContextMenuHandlers
HKEY_CLASSES_ROOT\Folder\shellex\ContextMenuHandlers\


Also if you want to a specific extension file

HKEY_CLASSES_ROOT\.xls