[CentOS-virt] Profiling tools

[lists at zfobjects.com]

I'm wondering if anyone has suggestions for profiling tools (RAM, CPU,  
disc IO) suitable for helping estimate the resource requirements of  
physical machines destined for virtualisation?

Preferably open source, and capable of running on Linux or Windows,  
but anything at all really.

I know that CentOS has a suite of "sysstat" utilities and /proc files  
that can probably provide the answers, I am looking at scripting  
something up with them if necessary.