Steve Jin: VMware VI and vSphere SDK
Steve Jin ( www.doublecloud.org ) focus is on the VI Java Toolkit. However the books also includes a great general introduction of the vSphere API and lots of UML-diagrams of the API data model. Both is very useful when you develop vCO scripts interacting with vCenters
see also http://www.amazon.com/VMware-VI-vSphere-SDK-Infrastructure/dp/0137153635
(Of course, you can find examples all over the web, but in most cases searching in the internet costs more time and distracts more than simply open the reference book on the marked site ).