The Zenoss team publishes a Community ZenPack Development page at http://community.zenoss.org/community/developers/zenpack_development. Here you'll find examples and techniques.
The Zenoss Developer's Guide provides an overview of Zenoss Core's architecture, data structure, programming techniques, and API documentation. You'll also find good reference material for zendmd, event processing, and more.
Developing for Zenoss Core and ZenPacks are topics that deserve their own book. We're only touching the fringes of those topics here.
You can find the Developer's Guide at http://community.zenoss.org/community/documentation/official_documentation.