Quartz provides an interface (ISchedulerPlugin) for plugging-in additional functionality.
Plugins that ship with Quartz to provide various utililty capabilities can be found documented in the Quartz.Plugins namespace. They provide functionality such as auto-scheduling of jobs upon scheduler startup, logging a history of job and trigger events, and ensuring that the scheduler shuts down cleanly when the virtual machine exits.
When a trigger fires, the Job it is associated to is instantiated via the JobFactory configured on the Scheduler. The default JobFactory simply activates a new instance of the job class. You may want to create your own implementation of JobFactory to accomplish things such as having your application's IoC or DI container produce/initialize the job instance.
See the IJobFactory interface, and the associated Scheduler.SetJobFactory(fact) method.
Quartz also provides a number of utility Jobs that you can use in your application for doing things like sending e-mails and invoking remote objects. These out-of-the-box Jobs can be found documented in the Quartz.Jobs namespace.