Tek-Tools Virtual Profiler
http://www.tek-tools.com/virtual/overview.php
Product technical brief available here. (Registration required)
Pricing is per host, with a required base framework as well. A starter pack with the framework and 3 host licenses retails for $4495, with additional hosts at $995. This tool runs on top of windows, so count that in your cost estimates.
The evaluation license will monitor two hosts. You can point it to a vCenter, and it will only monitor two hosts - but you can choose which ones are included.
This tool works by pulling events and data from virtual center (and the hosts) and wrapping some meaningful statistics around it. Virtual Profiler is an enterprise-class monitoring tool, with enterprise-level features. See the technical brief (above) for the whole feature set. The performance monitoring and other features are great, with very detailed information available for an array of components. Capacity planning is where this product gets interesting. Rather than run a report that shows you utilization graphs, this tool continually monitors the resource usage, and has a running counter of how many additional VMs can fit, based on average usage. This is easily viewed from a cluster or individual host level. There is also a nifty load simulator, where you can put in an expected number of VMs and disk space, and it will tell you how full the cluster will be. Keep in touch for my findings on VKernel Capacity Analyzer.

-Bruce Heavner, GlassHouse Senior Consultant