Hi,
I prepared template for ESXi. It works with 5.0, 5.1 and 5.5. You can graph:
vhosts - number of hosts, running, installed vm client tools
Logged in Users and number of processes
Real Memory - on 5.1 and higher
Processor load for every CPU core (strange works on 5.0, better on 5.1, fine on 5.5)
HW - state of Logical volumes, FANs, … (does not make sense graphs hw with state unknown (only running(2), warninkg(3)) and make threshold)
Disk usage
Interface statistics
You need enable snmp (yes, ESXi include snmp), read readme.txt