The only commercial tool I've heard people excitedly rave about is Veeam, which is specifically targeted at backing up VMs. The big feature draw of it is that

The only commercial tool I've heard people excitedly rave about is Veeam, which is specifically targeted at backing up VMs. The big feature draw of it is that it backs up the .vmdk image files directly, and incrementally. And you can spin up a VM directly from a backed up image without having to restore it first.