VMware ESX 3.x / VI3 provides a variety of methods for collecting critical performance and configuration data, including SNMP, Syslog, ESXTOP utility (via ssh), the SDK Web Service and the now deprecated ESX COM API.

Jonathan Hambrook has created a very nice 60-page how-to guide taking users through the configuration process of discovery and configuration of basic (and free!) ESX monitoring using SNMP and Telnet. He put many hours into this no doubt. You can down his guide HERE. Very well done Jonathan.

With no budget this is a great start. For those who can spare an extra $975 US (retail), nWorks offers a full-featured ESX management pack leveraging all the available data sources, most importantly the SDK Web Service, which is a very rich data source in the latest release. For a demo of the nWorks offering, see the demo on their product homepage at: http://www.nworks.com/vmware/