Which version are you running?
I'm running 5.1 in my lab here, and when I select the cluster, go to performance tab and click on view I can select "Resource pools and virtual machines".
This view shows the CPU and Memory usage of the resource pools in the cluster.
As this view is available in the 5.1 vSphere client, I'm almost certain that this view is at least in the 5.0 vSphere client. VMware development focus is on the web client and did not develop new features for the 5.1 vSphere client.
In vSphere 4.0, I believe there was a chart in the resource allocation tab of the cluster showing the CPU and memory usage.
Unfortunately the charts in 5.0 and 5.1 only show MHz and MB, not percentages. A feature request would be helpful from your part. I will include this feedback in my reports