A small Orchard API reference: Orchard Cheatsheet
The Orchard Cheatsheet is a nice little API reference for some lesser known objects, made by Orchard's lead developer, Sebastien Ros. The cheatsheet's list only contains elements of the API that are accessible from (sometimes very specific) shape templates (well, ExtensionDescriptor seems to be an exception), but e.g. WorkContext is something you definitely encounter elsewhere too.