VKernel Capacity Analyzer
http://www.vkernel.com/products/CapacityAnalyzer
Product Data Sheet available here.
Pricing is $199/socket. VKernel is a certified virtual appliance, so no Windows licensing is necessary.
Evaluation licensing is a 14-day license, and will manage one vCenter or 3 hosts. In my eval, it is pointed to a vCenter, and sees the 8-host cluster with no problem.
This tool also interacts with vCenter to gather its information. However, what it does with the information seems to be a bit unique. As you might expect from a product called Capacity Analyzer, performance is monitored from a capacity standpoint, and not a resource standpoint. You might think those seem the same, but they are different enough to mention it. Where as other tools have a lot of views centered around performance, and you can get to capacity, VKernel is centered around capacity, with the performance statistics as a secondary piece of the puzzle. The main overview screen lists highlights of: current and future bottlenecks, capacity availability, and top resource consumers. Then there is the expanded “Capacity Availability” view that just shows you what you have available. You can drill down at any level to find out more of the raw performance and utilization data used to create the capacity categories. You can even create your own groups of VMs, and view capacity data based on your custom grouping. At every level from Virtual Center to Cluster to Host, the same capacity views are available. This makes it incredibly easy to see how many VMs will fit in your environment.
Summary
So - there are five tools to consider when monitoring your VDI, or really any virtual environment. These are not specific recommendations, just some high level information in my opinion. As I’ve said previously, these are not the only tools, and you may find others that you like better. If you have other preferred monitoring / capacity management tools, please leave a comment and share your experience.

-Bruce Heavner, GlassHouse Senior Consultant