Monitor datastore utilization of VMware ESXi 4.X and 5.X via using the "Browse datastores on this host" page of ESXi's built-in HTTPS service.
This eliminates the need to manage a plugin that uses VMware's labyrinthine RCLI or the vCenter alarm framework, both of which have problems.
Simply add a list of hosts (and a login name/password) to the script and run it. This script connects directly to port 1984 instead of calling "bb" from the shell, so you can either run it as a plugin or run it standalone -- even on another host if you want to.
This plugin is compatible with Big Brother and it is also compatible with Hobbit/Xymon. Its output simulates that of unix "df" closely enough that if you are running Hobbit/Xymon the utilization graphs will appear as expected.
License: open source; GPL v3.