Scope Explorer is a free tool from VKernel that analyzes and visualizes the entire virtual environment across:

- Resources - CPU, memory, storage, network
- Data centers, clusters, datastores, host, virtual machines

Identify peformance, capacity, and resource efficiency issues in your virtual environment based on analysis from VKernel's Capacity Analytics Engine. This powerful visualization capability, displaying the results of intensive analytics of 20 key VM performance metrics, provides a number of important capabilities for a virtualized data center's staff.

http://www.vkernel.com/products/vscope-explorer