Please refer to the table below for a selection of useful tools and utilites which relate to VMware vSphere and VCP:
Tool
URL
Nagios
http://www.nagios.org/
PowerGUI
http://www.powergui.org/
Quest
vFoglight QuickView
http://vizioncore.com/free/vfoglight-quickview/download
RVTools
http://www.robware.net/
SolarWinds
VM Console
VM Monitor
http://www.solarwinds.com/products/freetools/vm_console.aspx
http://www.solarwinds.com/products/freetools/vm_monitor.aspx
Trilead
VM Explorer
http://www.trilead.com/
Ultimate Deployment Appliance
http://www.ultimatedeployment.org/
veeam
Monitor Free Edition
http://www.veeam.com/esxi-monitoring-free.html
VKernel
Capacity Modeler
SearchMyVM
http://www.vkernel.com/products/capacity-modeler/overview
http://www.vkernel.com/products/search-my-vm
vGhetto scripts
http://communities.vmware.com/docs/DOC-11965
VMTurbo
Community Edition
http://www.vmturbo.com/downloads/community-edition/
VMware PowerPack
http://powergui.org/entry.jspa?externalID=1802&categoryID=21
vSphere Mini Monitor
http://nickapedia.com/2010/02/15/vsphere-mini-monitor-now-with-more-cowbell/
Xangati for ESX
http://xangati.com/products/xangati-for-esx/
Xtravirt
vAlarm
http://xtravirt.com/valarm-free-desktop-tool-for-monitoring-vcenter-alarms