Fundamentals of vSphere Performance Management

http://www.doublecloud.org/2010/03/fundamentals-of-vsphere-performance-management/

Performance monitoring is a critical aspect of vSphere administration. This article introduces you the basic concepts and terminologies in vSphere performance management, for example, performance counters, performance metrics, real time vs historical statistics, etc. Much of the content is based on my book VMware VI and vSphere SDK by Prentice Hall.
Once you understand these basics, the related tools and APIs should be relatively easy. If you are already familiar with vSphere Client performance monitoring or esxtop, they help as well.

Performance Statistics (PowerCLI) 
http://www.sandfordit.com/vwiki/Performance_Statistics_(PowerCLI)

Performance Statistics (Perl SDK) 
http://www.vmware.com/vmtn/technology/developer/webinars/vi-perl-toolkit_webcast_2006-10-11.pdf

WAN Optimization for the Masses

The free virtual appliance version limited to two end points and 4Mb of traffic.

http://www.vx-xpress.com/

vSphere 5.0 Hardening Guide - Public Draft

http://communities.vmware.com/docs/DOC-19056

ControlByWeb Ethernet I/O

http://www.controlbyweb.com/

ControlByWeb Ethernet I/O products provide an easy and reliable way to monitor & control devices over a network.

vSphere 5 Host Network Design - 10GbE vDS Design

http://vrif.blogspot.com/2012/04/vsphere-5-host-network-design-10gbe-vds.html

ESX 5: Command Line VM Manipulation

http://blog.allanglesit.com/2012/04/esx-5-command-line-vm-manipulation/

Using esxcli to Mask a LUN from ESXi

http://www.virtuallanger.com/2012/05/01/using-esxcli-to-mask-a-lun-from-esxi/

VMware Health check - RVTools

If you don't have access to VMware Health Check Analyzer then other tool that can be used for VMware health-check engagement is RVTools.  It is free and has been around for about four years.  The author keeps it updated and once you connect to  vCenter or a Host you can export everything directly to an Excel spreadsheet.  The latest version is v3.3 as of April 12, 2012.

Google: RVTools
RVTools Homepage: http://www.robware.net/
Download Link: http://www.robware.net/download/RVTools.msi