A few months ago I transitioned us from VMware Server to VMware ESXi, booting off of a USB flash drive. If you don't know about server virtualization, VMware ESXi is a great way to get your feet wet, and it's a stable, production-ready (IMO) product.
However, one of the things that eluded me (in both the "Server" flavor and the "ESXi" flavor) was proper monitoring. Sure, I could setup data on each guest VM, but that didn't give me any info on the host.
I'm just downloading it today, but if it does what the "Features and Benefits" page says, then this will be a new must-have in my toolkit. More updates to come (hopefully) as I try it out.