Bradley Millington recently talked at Tech Ed Europe about Orchard. His first talk introduced Orchard CMS and its features. In the second he went into more depth about how to extend Orchard. If you've not heard of Orchard before these two videos are a great way to get up to speed.
Building websites with Orchard
View and download Building websites with Orchard files.
Deep dive into Orchard extensibility
View and download Deep dive into Orchard extensibility files.