This free tool, LPAR2RRD collects performance data and generates actual, historical and future trends utilization graphs of your virtual environment. It is agentless (it receives everything from the management stations like vCenter or HMC).
The product supports IBM Power Systems™ and VMware virtualization platforms. Collected data set can be extended to data provided by the OS Agents or NMON files.
The only problem, only to me, is that it can only be hosted on any Unix based operating systems. If you like me, a Windows guy most of the time, you may pass. 🙂