You should try RVTools if your not using it already
I know that RVTools has been around for awhile, but for those of you who have not had a look at this tool should download it. Its a nice little tool that you can install on your workstation and point it to your Virtual Center server or a single ESX host. The app then pulls down a ton of valuable information about your virtual machines and different status items about the ESX host. Most of these settings can be adjusted to meet your thresholds.
To list just a few of the items you can look at. You can see a list of VM’s with expired VM tools, datastores with low free space and many other settings.
You can download this tool from Rob’s site here. The application is free but be sure to spread the word and you can toss him a few dollars on paypal also.